Check the oil cap for an unusual amount of crankcase vacuum
No more oil screen behind you
Change the oil
This article is one in a series that have been released in conjunction with Wayne's
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contains 312 pages of full color projects detailing everything
from performance mods to changing your brake pads. With more than 950+ full-color
glossy photos accompanying extensive step-by-step procedures, this book
is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website
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The engine air-oil separator is an emissions device located on the top right rear corner of the engine. The separator is responsible for collecting residual gases and vapors contained inside the crankcase and funneling them back into the intake manifold where they can be burned in the combustion chamber. This reduces the overall emissions of the engine.
When the separator fails, you will begin to see a large increase in the overall vacuum in the engine crankcase. In the most extreme cases, the air-oil separator fails to separate the oil from the air, and oil is then sucked into the intake manifold. Oil in the intake system is not healthy for the engine and it can foul spark plugs and destroy catalytic converters at the very least. The failure of the air-oil separator is often (but not always) accompanied by huge amounts of white smoke exiting the vehicle's exhaust and a generally poor running engine. You may experience a check engine light (CEL) as the oil being drawn into the intake can affect the mixture level. The oil cap may be very difficult to remove when the engine is running due to high vacuum levels. In addition, you may hear a high-pitched squeal from the engine when it's running: this is caused by air being sucked in past the crankcase seal due to the extreme vacuum inside the case.
The proper method to test for the failure of the unit is to measure the engine crankcase vacuum with a slack tube manometer. Normal crankcase pressure, measured at the oil filler cap ranges from about 4-7 inches of water (drill a hole in the top of an old oil filler cap and attach the gauge there). When the air-oil separator fails, the intake manifold vacuum will draw into the crankcase and the levels will reach 9-12 inches or more. If you don't have a slack tub manometer (most of us don't), then you can use a standard vacuum gauge and/or get a rough feel for the level of vacuum pulled by comparing it to a normal running car.
If you're still not sure, you can take a closer look at the hose that connects the air-oil separator to the intake manifold (yellow arrow, Figure 1). If the unit is failing, then there will be a significant amount of oil or residue in this tube. If the car is running rough, then removing this tube and blocking off both ends should disable the system and restore previous performance. This is not a long-term fix, but instead a short-term diagnosis step to use before you replace the air-oil separator.
There is also a motorsports air-oil separator available that you can use on dedicated track cars (2003 and later). This special separator is designed to work with the higher g-forces that are exhibited with high speed track driving. If your engine has a lot of blue smoke exiting the tailpipe after driving on the track, you may need this upgrade. See the 101Projects.com website for a copy of the Porsche bulletin explaining this upgrade.
Shown here is a new air-oil separator unit for an
early Boxster. The purpose of the separator is to
separate fuel vapors from the crankcase and funnel
them back into the intake. The air-oil separator is an
emissions device, and although its presence doesn't
hurt performance, if it fails or if one or more of the
vacuum line connections develop a leak, it can
negatively affect engine performance. There have
been many updates to the unit over the years. The
later-style units are a direct bolt-on replacement,
but the hose that connects the air-oil separator to
the throttle body has been updated as well (the old
one is a little too short). If you are replacing your
air-oil separator with a new one, be sure to install
the updated connecting hose as well.
With the engine compartment lid open, it's fairly easy to gain access to the air-oil separator connections. The green arrow points to the separator. The yellow arrow points to the connection that leads to the intake. This is where vacuum is pulled from the intake manifold. Simply squeeze this connector and pull it off to disconnect it. The purple arrow points to the somewhat hidden flexible hose at the bottom of the separator. I found this connection easiest to disconnect from below (see Figure 3).
With the car on jack stands, you can poke your head up into the chassis and get a better view of the separator. The green arrow points to the separator itself. The purple arrow points to the quick-disconnect vacuum line that leads to the opposite camshaft housing. The red arrow shows the right side of the transmission. The light blue arrow shows the flexible hose that connects the separator to the right side camshaft housing. I recommend replacing this hose along with the separator. Removing the little spring clamps that attach this hose is probably the most difficult part of the entire task: use a set of special pliers specifically designed for the task. Finally, the whole unit is attached to the engine case using two bolts shown by the yellow arrows.
Comments: I have an 02 Boxster and just in the process of completing an engine out and rebuilt in, and have been looking for a an article that will point me in the right direction so that I don't spend alot of time looking for a couple of connection questions. first the line coming off the oil cooler, where on the coolant system does that connect to, and the a/c clutch elect. connection location? doing a few items including those tomorrow.
October 12, 2014
Followup from the Pelican Staff: A/C clutch should be located in the right side rear fender, there is a group of electrical connectors there. The oil cooler, heat exchanger line should connect to a small hose that Ts off a larger hose. - Nick at Pelican Parts
Comments: I just changed my AOS and cleaned the throttle body on a 2000 Boxster S. I am having a hell of a time getting the air intake tube back onto the throttle body. Would you have any suggestions on how to get this tube back on. I must of spent at least 1 hour trying with no luck.
September 18, 2014
Followup from the Pelican Staff: Be sure the clamp is backed off, then coat the inside of the duct with dish soap. It should slide on. - Nick at Pelican Parts
Comments: I own a 1997 boxster that has 54,000 miles...I have owned for 4 years and noticed a little smike at start up since i owned it...I paid the car off last month and had my first real issue....coolantbin trunk...I replaced my coolant overflow bottle a week ago and after I did I had a cel...found my oil cap to be loose...as soon as I tightened all was good...well a few days later cel came back on for a bunch of misfire codes po300,po306, p0304 ,p030 p1130, p1128 p0130, p150...plus p1319,1318,p1316,p1317...I changed all my plugs all that i removed looked great one cracked coil. Then I removed my mass air flow sensor and cleaned it...air hosed my air cleaned that looked great and vacuumed the air cleaned case...removed both battery cables and then re connected...went for a ride went about 1 mile and all of a sudden white smoke everywhere...cel flashing barely running...limped the car home and discovered excessive oil coming out exhaust :- read about aos and removed the tube you described above to see if it was coated in oil...it was loaded with oil...procedures to remove all the plugs I just installed and they were all covered in oil...I removed the aos in about 20 mins thanks to your article andics...plan on replacing tomorrow...with so much oil coming out the exhaust will I have to replace the the cats and o2 sensors? Could I have damaged my rings? :-
September 4, 2014
Followup from the Pelican Staff: You may have filled the exhaust. Give it some time to burn off. The engine should be OK. - Nick at Pelican Parts
Comments: Good day Nick,
I have replaced the AOS on my Boxter 2.5, 1998. It was fine for about a week. However what I am experiencing now is that suddenly the white smoke is back after driving it for about 15 minutes and also the engine cuts out as soon as I take my foot off the accelerator and I have to restart. I experience a different symptom = if the oil cap is on and I rev the engine, it also cuts out. When I remove the oil cap removed easily, the engine starts running normally and does not cut out, but I hear a lot of rumbling noise coming from the oil intake. I have removed the P-pipe and I can feel a bit of oil very little, but please note that the car has been standing for around 12 hours. Any ideas please?
September 1, 2014
Followup from the Pelican Staff: You may have a faulty crankcase breather. i would check crankcase vacuum to see if it is too high. - Nick at Pelican Parts
Comments: I have a 2005 Boxster S. When I was driving down the expressway today it was making a high-pitched whine like a belt was about ready to throw esp at low rpms but my gauges showed in the normal range and no check engine and engine seemed maybe a little rough but not bad. When I got to my house I noticed a burning smell and figured it was a belt. When I went to start the car back up again after a bit a ton of darkish white smoke was exiting the tail pipe. At first I thought oh no, a blown head gasket or a cracked head but again, no temperature issues and it seemed to calm down a bit after running at idle but was still running rough. I came here and found this article. I don't have a pressure gauge handy but I did try to remove the oil cap and couldn't. I shut the car off, then removed it and started it back up. It ran like garbage at idle and almost shut off. If I put my hand over the oil filler pipe it was sucking my palm in so hard I still have a pretty good indentation in my palm 15 minutes later and it definitely took a little effort to pull my hand away. Given what I'm reading here it sounds like this is almost definitely the AOS. I can go pick up a gauge tomorrow to test but I'm honestly just thinking about ordering the part and replacing it. Anyone feel like this is a pretty safe bet?
July 30, 2014
Followup from the Pelican Staff: I would agree, it sounds like the AOS is the problem. The gauge is the best way, be prepared to replace it. - Nick at Pelican Parts
Comments: Hi Nick, thanks. In your reply you mention having a spare around in case the lower red o-ring that goes into the engine is damaged from the AOS being seated incorrectly July 21, 2014. Could you let me know which part # this is so that I can order it? Thanks.
July 23, 2014
Followup from the Pelican Staff: I don't have part numbers handy, our parts specialists can help with that. Give our parts specialists a call at 1-888-280-7799 - Nick at Pelican Parts
Comments: Hello, recently out of nowhere, I was driving my '98 986. Came to a parking lot for about 10 minutes and shut the car off. After those 10 minutes, I started the car, and the engine rev's between 1000-2000 rpm every 2 seconds. Even when I'm driving, the car opens the throttle on it's own and speeds up. Would replacing this fix this problem, or should I look into other things. I don't want to mess with my car until I know I can fix it. Thanks.
July 23, 2014
Followup from the Pelican Staff: AOS could be your issue. I would start by checking the engine for vacuum leaks. If none are found, the AOS may be it. - Nick at Pelican Parts
Comments: Hi, I bought the AOS and have installed. But I now have a loss of power at 4000 RPM+. The car is a 2000 Boxster S. In the picture I have attached, you can see that there is a red o-ring visible from the outside of the installed AOS. I don't remember the old part having an outer o-ring. Could this be the issue??
All the other hoses appear to be seated correctly. Any direction you can provide would be greatly appreciated! Thanks.
July 21, 2014
Followup from the Pelican Staff: The O-ring is not seated correctly. I would remove the valve, then lubricate the O-ring with dish soap and reinstall it. Have a new one on hand in the case it is damaged. - Nick at Pelican Parts
Comments: I have a 99 Porsche Boxster that is mixing water and oil. The car is overheating and the mixture is exiting the water tank in the trunk area. I had the air oil separator replaced, but the mechanic was unable to flush the system supposedly because he couldn't get enough suction due to the clogging. I don't know if this is fixable or if I should just sell the car for parts. I really know very little about cars so any help is greatly appreciated.
July 11, 2014
Followup from the Pelican Staff: I would pressure test the cooling system. If the system will not hold pressure and there are no external leaks the head gasket may be faulty. - Nick at Pelican Parts
Comments: I cannot get the new aos o-rings fully seated in the crankcase of my 986. Tell me that's normal because I have given up after 8 hours.
June 29, 2014
Followup from the Pelican Staff: None of the O-rings will go into the crankcase? Try lubricating them with dish soap or liquid hand soap. - Nick at Pelican Parts
Comments: Hi Wayne, I have a 2001 Boxster S with 60,000 miles that is exhibiting the classical blue smoke AOS challenge. I replaced the AOS last year, and the back pressure on the crankcase is still measuring 5 1/2 inches of water. Everything seems to be functioning normally yet I still get the occasional blue smoke.
I have discovered that I can "provoke" the problem by taking very aggressive left-hand turns under full throttle. As the AOS sits on the right-hand side of the engine, I have come to the hypothesis that crankcase oil is being pushed against the right side of the engine, and during shifts at full throttle the high spikes in vacuum pressure will actually suck the oil up the drain tube and into the intake manifold.
To correct the problem I am considering bypassing the AOS and treating it like an old fashion PCV valve. Thus, placing a small air filter on the vacuum port leaving the AOS, and capping the vacuum port on the intake manifold. I could easily return it back to factory design at any point in time.
Aside from the obvious slight increase in emissions, are there any other harmful side effects that you can think of? The fix seems to be obvious, yet after much web searching I could not find anybody that has suggested this, or tried this. Maybe I am over simplifying the solution, or oversimplifying the function of the AOS.
I know you get about a billion questions on AOS on the boards. Thanks for reading this and offering your thoughts.
June 29, 2014
Followup from the Pelican Staff: There is an issue with track cars and smoking. If the breather is tampered with beyond the factory setting, it could fail an emission test. I would look into the solutions the track guys are using, you may find something helpful in our forums. Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
Comments: It acts like the AOS is the issue. The idol fluctuates between about 700 and 1100. After gets up to temperature and you shut it off it will not start until it cools back down. And lately when it gets up to temperature it will actually shut down if the RPMs get too low. The grommet on the part going into the crank case was visible and pushed back before I removed it. Could this be my issue? I included a picture.
June 13, 2014
Followup from the Pelican Staff: Hard to say without seeing the fuel trim data. If it wasn't sealing, the engine will run poor. - Nick at Pelican Parts
Comments: I have removed my AOS but I'm not 100% it's the problem. Is there a way to troubleshoot once it has been removed?
June 12, 2014
Followup from the Pelican Staff: Off the engine, there is no test. The valve has to be under pressure from the engine. Then a crankcase pressure reading is measured. - Nick at Pelican Parts
Comments: On any technical "how-to" article on automotive repair, I have found it VERY helpful when the size and type of fasteners are mentioned. For example, it this AOS article it would have been nice to know the size and type the two "bolts" securing the AOS to the engine. Saves a lot of trial and error.
June 10, 2014
Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
Comments: Having recently purchased a 1999 Boxster I noticed white smoke on start up and proceded to change oil separator and found that one of the spring clamps on the flexible hose was actually a regular hose clamp. I am sure that this is not recommended but would it effect the function of the oil separator in any way and would it contribute to the failure of the separator?? I also replaced the hose clamp with the correct spring clamp.
June 7, 2014
Followup from the Pelican Staff: A standard hose clamp should nt cause the separator to fail. - Nick at Pelican Parts
Comments: Hi chaps, I recently 4 weeks ago bought a 08' cayman S from a used car garage, they only sell sporty/prestige stuff and the service seems to be of a high standard.
I'm a ex mechanic myself, so I had a good look over the car myself before purchasing and a very detailed look through all the service history.
It has full porsche service history and all previous invoices are present.
I am confident it's a well looked after vehicle as far as service history and bodywork are concerned
Anyway, getting to the point.
It was my 3yr anniversary with the mrs yesterday so I went for a drive out and some pub lunch with her, we headed up to the evo triangle in Wales as I'm a keen driver and have always wanted to go.
I was driving the car hard when I suddenly got a huge plume of blueish/white smoke from the exhaust and a brief loss of power. I slowly drove the car to somewhere I could pull in to have a check. It drove fine with no cel light, no untoward noises. The smoke cleared and all seemed ok. I sat with the car idling for a moment and had a good look around, no untoward noises or oil leaks/spills present. So I turned the engine off and checked the oil level, it was full so I started the engine again, big puff of smoke which soon cleared on idle. Still sounding healthy, I pulled out of the car park and nearly immediately if gave a large misfire pop and the engine cut out.
I once again had a look around for anything obvious limited by lack of tools and no access to the engine. All looked ok.
I tried starting it again and it's just started and cut out immediately, if I started it and kept it revving the engine still sounded healthy and running on all 6 cylinders with no cel light. I called and joined the AA as I was 86 miles from home, the chap arrived within an hour.
I described the fault and showed him how to gain access to the engine, we both had a look around but the only thing that looked untoward was the intake pipes seemed to have popped of and where not fully seated home on the underside of them. We put them back in place and it started and ran fine, I drove it home and all seems ok since that.
My concern is-
A. What was the large plume of smoke?
Maybe I over whelmed the air oil separator with high cornering speeds?
B. Was the big misfire what caused the intake pipes to pop off and stop it running? If so is there an underlying fault still lurking?
Any help would be very helpful as I'm not to knowledgable on these cars.
Thanks in advance!
April 28, 2014
Followup from the Pelican Staff:
. What was the large plume of smoke?
Maybe I over whelmed the air oil separator with high cornering speeds? this could be the case, keep an eye on it. Or have crankcase vacuum tested. This is the best way to determine if the AOS is faulty.
B. Was the big misfire what caused the intake pipes to pop off and stop it running? If so is there an underlying fault still lurking? the mbackfire may have caused the pipe to pop off, this is not uncommon result of a backfire. It may have been caused by the oil consumption issue.
Be sure to check engine oil level.
- Nick at Pelican Parts
Comments: I Successfully installed Lower AOS Vent Line: by removing the three bolts securing CAI, and removing the left rear wheel well cover. I did not have to remove CAI, just the botls to allow the CAI a little freedom to be moved around. I also connected the new AOS ventilation connection to vent line before securing to crank case. Not an easy job to say the least, im beaten battered and bruised. Saved a trip to the dealer, PRICELESS!!!
April 17, 2014
Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
Comments: @Blackops- Dude you rock, That photo is worth it's weight in gold sir! Any luck finding a good way to access the connection there? I am engineering some rubber tubing couper repairs for this hose in the interim, hope it wont be hard to replace in the future! Any one have experience using rubber tubing to repair these rigid
April 13, 2014
Followup from the Pelican Staff: Glad you got it worked out. - Nick at Pelican Parts
Comments: Blackops- Thanks, I will go look in a bit see if I can find it, can I get a photo of how it was routed over there from AOS to connection? Essentiall the belt side of the engine as well?
April 13, 2014
Followup from the Pelican Staff: SOunds like you got it worked out. Thanks blackops for the help. - Nick at Pelican Parts
Comments: Pics of where lower vent line from AOS connects to engine. The locations is a beast to get to. The connection is under left intake manifold. Please any suggestions in regards to making the connection is greatly appreciated. Should I remove air intake box? Can I gain access to make connection through the wheel well?
April 13, 2014
Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
Comments: IAN FORBES....We are tackling the same beast. Hang in there, I know what you are talking about. Perfect timing, I will take pics. Its not impossible, we just need the correct solution. Hang in there. Pm me or send email addy. Thanks.
April 13, 2014
Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
Comments: Help! Any idea how to intasll the LOWER Vent Lint to AOS.? I replaced AOS, upper vent line, Oil filler tubes x2 from firewall to engine. But i ran into a snag. I was able to snake the lower vent line, hiwever no room to get enough pressure to connect to engine. Intake manifolds are loose, but not disconnected from fuel rail...should i remove fuel rail or air intake behind driver?
April 13, 2014
Followup from the Pelican Staff: SOunds like you got it worked out:
I Successfully installed Lower AOS Vent Line: by removing the three bolts securing CAI, and removing the left rear wheel well cover. I did not have to remove CAI, just the botls to allow the CAI a little freedom to be moved around. I also connected the new AOS ventilation connection to vent line before securing to crank case. Not an easy job to say the least, im beaten battered and bruised. Saved a trip to the dealer, PRICELESS!!!- Nick at Pelican Parts
Comments: Can someone upload a photo of where the purple arrow hose connects to the opposite side of the camshaft housing? I am taking over after my mechanic abandoned me, the new AOS is in but I cannot figure out where to connect the engine side of this hose. Thanks to anyone who can help. I have found the catalog image but does not show where this connection is actually located...
April 13, 2014
Followup from the Pelican Staff: Sounds like blackdrops got it worked out for you. - Nick at Pelican Parts
Comments: hi its my 2nd time to replace AOS in less than 20km of running.i drive a 2000 boxter S. what could be the problem? i have replace all recommended parts by the parts department
March 25, 2014
Followup from the Pelican Staff: I would check if there is a restriction in the crankcase causing repeated failures. - Nick at Pelican Parts
Comments: Hi, I iwas trying to replace the aos on my boxster 2002 but i broke the lowerr fitting vent tube. How do i replace it cause it looks very hard to replace due to all the things i have to remov?
March 20, 2014
Followup from the Pelican Staff: You may have to remove the intake manifold if you cannot get to it. Can share a photo of the broken part? - Nick at Pelican Parts
Comments: what are the different symptoms between bad head gasket and faulty AOS? would appreciate it very much if anyone could share your knowledge and experience. William D
February 21, 2014
Followup from the Pelican Staff: a Head gasket causes smoking and overheating
AOS causes smoking and oil consumption. - Nick at Pelican Parts
I have a Porsche Boxster S 2004. During this month in 3 incidents cooling system rubber hoses busted.
When I open water reserve tank cap, lot of gas is released is it normal? I feel cooling system is too pressurized, is it a correct assumption?
Appreciate if you could let me know what causing these rubber hose leaks.
February 18, 2014
Followup from the Pelican Staff: If the cooling system is leaking, I would pressure test the cooling system. If the system does not hold pressure and there are no external leaks, you may have a faulty head gasket.
Hoses wear at the same rate. If you replace one, the others are not far behind. I recommend replacing hoses in sets to prevent consecutive hose failures. - Nick at Pelican Parts
Comments: I just did this on my 2006 Cayman S. It was actually quite easy - 2 e-torx head bolts removed from above, 3 of the pinch to remove clamps the spring clamp on the rubber hose going to the engine block.
I ended up removing the hose from where it went to the engine block and then removed it from the AOS off the car. All the work can be done from the top, at least in my Cayman. I'd imagine it's a bit harder in the Boxster as you have to lean over the fender. I pretended I was cargo and worked on it from the rear cargo area. :
All my work was done with the wheels on the ground.
February 10, 2014
Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
Comments: I have a 2009 Base Cayman with 34000 miles. I've noticed over the past few months random and excessive stinky white smoke at cold start, enough to fill the shop. It clears reasonably quickly, and does not smoke while driving. The oil was changed about 6000 miles ago, and I check it often. I've not seen a measurable drop on the "electric stick." Yesterday I did a number of short-trip errands without issue, but it felt like the power was down it goes alright, just not crisp in acceleration. This morning at cold start, the CEL came on. Reading your article, I do recall hearing a high-pitched whine on first start after garaging it for a week or so during bad weather excessive crank case pressure? I pulled the oil cap while running...significant vacuum pull and the idle is very rough This was expected, the vacuum was not. I will have the ODB II code read tomorrow, but I think I may have an AOS issue causing a mixture problem. Or could it be something else related? Your thoughts? In my research, I noticed there is a difference in the later model AOS mount points. Is there any specific difference in the replacement process? Special tools or pitfalls? What else should I examine in the troubleshooting process? I've only had the car a few months, and the PPE revealed none of these issues not surprised. Any additional guidance or advice is greatly appreciated.
January 16, 2014
Followup from the Pelican Staff: The procedure for replacement is different, but not too much. This does sound like it could be your problem, I would suggest checking fault codes as you plan to and crankcase vacuum. - Nick at Pelican Parts
Comments: What a day.. when white smoke ..just blow up in the sky...i thought it was AOS so i spend some time trying to get it out ....but it was hardly than i thought...so i check the air filter and my air filter was filled with water...so i dry it out and no more smoke...lol
January 12, 2014
Followup from the Pelican Staff: Thanks for the Info. We appreciate it.
- Nick at Pelican Parts
Comments: Hi All,
I've a 2001 S that I bought a few months ago. 75K miles. No signs of any smoke etc... runs perfectly.
It's got something funny going on that seems linked to the AOS but doesn't seem to be exactly the same either.
Basically, the first time I took the car out for a proper run and hit about 5k revs in third it blew the hugest cloud of white smoke out the back that I've ever seen on a car. I lifted off fearing I'd blown the engine, the engine light came on for 30 secs, and then everything was perfect again. Drove home and googled to find various threads about the AOS. I checked the oil filler vacuum, there was a slight sucking in of air, but not a huge amount.
So, I replaced the AOS over Xmas what a PITA job that was and the car smoked at start up for a few trips and the oil filler was now blowing slightly rather than sucking, so I assumed all was sorted.
Until yesterday when I went out for a drive across town. Everything perfect again until I hit 5k revs or so in second and the massive dump of white smoke happened again. It's a great effect, the baddies tailing me have no option but to brake and avoid it. So it does have it's advantages but not really something I want as a standard feature.
Oil level was showing as full when I first got the car and is now showing 1 clear bar to full.
Any ideas what this could be, I'm not convinced it is the AOS but maybe something else in the system that doesn't like the high revs and 'pops' allowing oil to get where it shouldn't be.
As soon as I lift off the smoke immediately stops.
Any advice much appreciated! :
January 6, 2014
Followup from the Pelican Staff: Under heavy acceleration, like track conditions, these engine will puff smoke once and a while. You may be experiencing a normal characteristic. Monitor your oil level to be sure it is not dropping down. If it nis not smoking at start up, I wouldn't chase it too far. - Nick at Pelican Parts
Comments: A/O S needed ?
I have a 80k miles 2001 boxster 2.7 which I have owned for 500 miles ! I have white smoke on start up which is worse after being left for a few days, but clears quickly. I have a DEL with codes 1128 and 1130. I looked on the forum and decided I need an A/O S, but just checked and there is very little vacuum at the oil filler easy to remove when the engine is running and seemed light vacuum when I put my hand on top. Does this still sound like an A/O S issue or something else. In addition there is a slight smell of coolant around the car and the level has dropped an inch in the top of the reservoir in 500 miles. Any advice welcome - I'm a complete novice to Porches but have wielded wrenches on other cars.
December 27, 2013
Followup from the Pelican Staff: If smoking at start up, it could be the start of a failing AOS. Might be best to replace it before it gets worse. - Nick at Pelican Parts
Comments: Is there a way for Air Oil Separator, High Performance Version to fit on 2000 boxster?
November 12, 2013
Followup from the Pelican Staff: There is a high performance oil separator for the 986 Boxtser. Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
Comments: I just did this job and I found that a small c-clamp works to remove the lower bellows clamp instead of a special tool or pliers. I simply used the c-clamp to open the hose clamp up and remove it. I reinstalled the clamp using the same method. This seemed to take a little bit more time than using a special tool but the results were the same.
October 4, 2013
Followup from the Pelican Staff: Thanks for the additional Info. We appreciate it. - Nick at Pelican Parts
Comments: Ok, I just did this and want to add some comments not made above.
Pelican mentions that there are two crankcase check valves 996-107-047-51-M100 that could lead to premature air oil separator failure. I could only find one. It was on the top left front of the engine under the intake. You can only see it with the engine cover behind the seats removed - and it's tucked in there. It was quite a task to get it off and out and replaced. But, it was covered in enough dirt that I decided to do it. FWIW, I unscrewed the bolt from the top with a very long extension and used one of those springy-finger grabbing thing to grab the bolt so it didn't fall. Then I pushed the valve and hose backwards, got under the car and pulled it down. I could swap in the new valve from there.
I spent a lot of time looking and could not find the other one. Anyone know? This is on a 2000 S.
Also, the replacement air oil separator came with a new flexible hose or bellows out the bottom of the separator. So, you don't need to buy one.
Also, the replacement crankcase check valves come with new o-rings. So you don't need to buy those either.
September 7, 2013
Followup from the Pelican Staff: Thanks for the additional Info and taking the time to share your experience. We appreciate it. - Nick at Pelican Parts
Thanks for the reply
Replaced the aos valve with genuine Porsche part but the oil smoke is still there on start up. Any other ideas?
Car runs spot on apart from this. Just looks terrible
August 26, 2013
Followup from the Pelican Staff: Thanks for the feedback. Glad we could help. If there is oil residue in your intake manifold or exhaust system, the smoke will last until it burns off. Could take one or two test drives.- Nick at Pelican Parts
Comments: While cleaning out the throttle body yesterday, I noticed more than a light coating of oil in the tube from the AOS. When I pulled off the tube off the throttle body see pic and stuck my finger in the bottom of the fitting on the throttle body, there was enough oil there to drip off my finger.
I've also been having to replace oil on a fairly regular basis, which I had been attributing to spirited driving.
No indication of blue in the exhaust, though...
Is the AOS due for replacement?
August 25, 2013
Followup from the Pelican Staff: If there is that much oil in the intake, the AOS is likely the issue. Not many other places for the oil to come from. I would replace it before it gets worse. - Nick at Pelican Parts
Comments: Yes Thanks Nick - I found access to end of pipe connection is best after removal of internal panel to engine inside car - the big problem is that the pipe is rigid so will be hard to replace as it threads over the engine top and through the intake manifolds. Got new pipe from Porsche to fit so I will have a go.
August 17, 2013
Followup from the Pelican Staff: Thanks for the follow up. We appreciate it. - Nick at Pelican Parts
Comments: Thanks Nick...Does anyone know the best / easiest way to get at the connection for this pipe? Looked at top of engine it cant be seen or reached...partly visible from underneath but looks as if inlet manifold would need to be removed after all the throttle body tubes and with all the wires sensors etc it looks daunting job
August 15, 2013
Followup from the Pelican Staff: If you remove the throttle housing and the crossover air pipes on the intake manifold, you should be able to get to it. At least a lot easier. - Nick at Pelican Parts
Comments: Good info...fitted new AOS but broke flexible pipe that connects to mid point of AOS body. Did temporary fix of supaglued rubber pipe inside flexible broken pipe so this has reduced to bore to about 6mm for about 3 inches - It works but then looked to see where the other end fits onto engine to install new pipeand its almost 99% inaccessable...Does this have to be fitted with engine out?!? Please advise
August 14, 2013
Followup from the Pelican Staff: This pipe can be replaced without removing the engine. I would replace as soon as you can. - Nick at Pelican Parts
Comments: My 1998 Boxster is throwing to codes: P1124 & P1126 in addition to a low output reading from my MAS. Reading on the two codes indicated that it could be an AOS issue. My questions is: if the AOS is an issue, could this also be fouling up the sensors on the MAS? Thanks.
July 31, 2013
Followup from the Pelican Staff: There would have to be quite a bit oil to reach the MAF sensor. It would have to work up theintake pipe, against pressure. I would guess not, but you never know. If you knwo the AOS is an issue, start there and see if your codes are rememdied. - Nick at Pelican Parts
Comments: Well, I just got done replacing my AOS on my 2002 Boxster S. it took 2 hours just like the tech article says, but reaching way up in from the bottom is more difficult than the pictures make it look. I recommend unbolting the little bracket holding a wiring harness under the blue arrow in figure 3 above. I also had more trouble with the "quick disconnect on the right side of the AOS. it's hard to pinch the releases and pull it off. Can't seem to get a good hold on it and my hands are not exceptionally large. I used short handled channel locks to squeeze the release and a long screw driver to apply prying pressure in the correct spot. Kinda tricky. I would say this was the toughest part for me. Once everything was loose, I pulled up on the AOS in the hopes of ripping/ tearing the bottom hose that is trash anyway new one is included with new AOS. However, it did not tear as planned. This ended up working out nicely. I left the tension on the AOS and came in from the bottom with my channel locks and when the clamp tension was released, the hose was freed instantly. I pulled the AOS out from the top. I inspected and cleaned up the area before installing the new AOS. Be careful not to get dirt into any of the exposed opening and hoses. I can only assume that it would be a bad thing. Lol. As for reinstall, I got the AOS positioned and kinda dry fit everything to make sure it lined up. Oh, make sure you reconnect any wiring harnesses that we're disconnected during removal. During the dry fit, I remembered one of them and HAD to pull the AOS to reconnect it. Dry fitting was a good idea. Reconnecting hoses was not bad at all. I had a little trouble lining up the holes to bold it back on to the side of the transmission where it attaches. Other than that, I did a test run for about 3 miles, got up to operating temp 180 degrees ish and rough idle seems to have gone away. My AOS was not completely shot like some of the mosquito foggers I saw on YouTube, but I'm convinced it was causing my rough idle at operating temp. I did occasionally get a puff of smoke at cold start prior to replacement, but this pre dates any rough idle issues. Porsche states a puff that clears in a few seconds is normal at cold start. I believe them. I have my oil analyzed at each oil change to test for contaminants. Cost about $18 for the test kit at NAPA Auto parts. Money well spent. I sleep better knowing I have zero coolant and abnormally high amounts of metal in my oil.
July 27, 2013
Followup from the Pelican Staff: Thanks for the additional information. We appreciate it. - Nick at Pelican Parts
Comments: Can I visually see if I have the old version of the AOS?
July 22, 2013
Followup from the Pelican Staff: It's hard to tell. You will have to check with what version the year of your vehicle came with, then buy the kit to install the new one. Which woul dhave the updated AOS and hoses, if needed. - Nick at Pelican Parts
Comments: Hi. Just purchased a 1999 Boxster 2.5
On start up it occasionally lets out a small puff of smoke and when it gets up to temperature it idles between 1100-1300 rpm, if I open the oil filler cap while its running it sounds like its sucking in lots of air. When I disconnect the MAF it stalls same when I disconnect the idle control valve plug. It is showing no error codes when plugged in. Does this sound like the symptoms of a failed AOS? Thanks
July 21, 2013
Followup from the Pelican Staff: It does sound like you have a faulty AOS. The best way to tell is to measure cranklcase vacuum. If the crankcase vacuum is out of spec, this indicates a faulty AOS. - Nick at Pelican Parts
Comments: It turned out that the "gallon" jugs of oil I aded were in fact 5 qts. so i overfilled by a qt. Hoping that is all there is to it.
July 5, 2013
Followup from the Pelican Staff: Thanks for the follow up. We appreciate it. - Nick at Pelican Parts
I have a 2007 boxster with 24k mls
Its a 2.7
The problem being cloud of blue smoke on initial start up then clears it runs ok and doesnt smoke on standard running only after being stood
July 3, 2013
Followup from the Pelican Staff: Some smoke after the vehicle sitting is fairly common. But it could also be the start of a failing AOS. If the problem gets worse, I would replace it. - Nick at Pelican Parts
Comments: The vac test is in inches of H2O? I blew smoke last weekend and it was checked using inches of Hg. It read about 7" and that would be I think like 94" H2O - lots of vacuum. But to the touch there wasn't an unusual amount.
I have the X51 3.8L in my '06 CS and thought I wouldn't have these issues. For the first time ever it is blowing smoke at the end of a straight after a 180* left hand hairpin. No CEL, no codes per PIWIS, no squealing. AOS or something else? Thanks
June 22, 2013
Followup from the Pelican Staff: The test is in inches of water. I usually see about 5".
If it is blowing smoke only after a turn, I would check the air oil separator. - Nick at Pelican Parts
Comments: Hi .I race a 2007 Cayman ,and i have a problem with the oil in the corners at high speed somebody ,told me this :If you drive your Boxster/Cayman on a track, certain conditions can cause a serious engine failure. High engine RPM's during high speed turns will cause engine oil ingestion. This situation will be further aggravated if race tires are being used.
Ingestion occurs when the air/oil separator is overwhelmed from the conditions mentioned, and oil is forced into an air ventilation hose. The result, oil is sent into the air manifold, which feeds oil into the engine cylinders. This causes extreme smoke from the exhaust, unusual back-fire type sounds, and can cause damage to the engine.
I am very interested in your opinion and if you have some part that will solve my problem or if this is the problem?
Thank you very much .
June 20, 2013
Followup from the Pelican Staff: There can be a problem with your AOS or you're just possibly overwhelming it. I have heard about an aftermarket solution, give our parts specialists a call at 1-888-280-7799. They can help you look into a solution. - Nick at Pelican Parts
Comments: Hi I was wondering if anyone knows how exactly the AOS works? is it vacuum or pressure activated?
June 14, 2013
Followup from the Pelican Staff: Pressure is built up in the crankcase from the increase in temperature and combustion blow by. As pressure builds the gases are drawn toward the AOS. There is slight negative pressure there from being connected to the intake system. As the oil moves through the valve liquid oil gets trapped in the baffles but the gases are allow to escape into the intake and get burned in the combustion process. - Nick at Pelican Parts
Comments: had a bit of hesitation in the motor and some white smoke. With oil cap removed it runs really rough and is drawing lots of air. Replaced the aos and not much change. did pick up some idle and no smoke but vacumme is still high and hesitation still prevails. there was huge goobs of oil in aos tube, no doubt needed replaced.
June 11, 2013
Followup from the Pelican Staff: White smoke is typically coolant or brake fluid. You may have a vacuum leak and with the oil cap removed your also letting more air in to the crankcase and therefore the intake through the now clean aos tube. Check for oil on your Mass Air Flow sensor. May have gotten there from oil being allowed into the intake through the old aos tube. - Nick at Pelican Parts
Comments: 2003 Boxster S, 60,000 miles. I am trying to diagnose a squealing sound and suspect the AOS. The squeal begins at about 25mph and doesn't vary in pitch with engine speed or car speed, ie it is a constant pitch. Below about 25mph it ceases. Any thoughts?
June 2, 2013
Followup from the Pelican Staff: This could be the AOS. However, I would try to pinpoint the noise to be sure. if the noise doesn't change with RPM or vehicle speed you might be on the right track. Try rasing engine RPM in Park, check if the noise can be duplicated.- Nick at Pelican Parts
Comments: Thank you Nick @ pelican parts the AOS and plugs I purchased sorted the smoke problem out. There was no need to crank the engine over with the plugs removed in the end, I removed the plenum/throttle body enough to clean out the large deposits of oil , using a lint free cloth and some carb cleaner. A short drive to heat up the cats and cylinder head 8miles and no more smoke.
May 31, 2013
Followup from the Pelican Staff: Thanks for the feedback. Glad we could help. The AOS can make quite a mess. - Nick at Pelican Parts
Comments: I have a 2003 auto tiptronic Boxster with 150k I bought new. In 2007 at 50k I had an IMS catastrophic engine failure and rebuild by dealer under an extended warranty plan. Since then I have myself replaced the fuel pump, water pump, brake rotors/pads, various fluids and routinely change oil and filter. Last week as I was pulling out of a parking lot and accelerating when I heard a "funny" noise immediately followed by an enormous amount of white billowing smoke from the rear exhaust? blinding all traffic behind me for a good 5 minutes until dissipated. I immediately pulled over and shut off the engine and then noticed a very small salad plate size oil puddle on the pavement beneath the exhaust. Checked the oil level on dipstick and found a little on the red rounded tip-end. Towed the car home and researched the problem. I'm fairly certain it is the AOS. Does that sound reasonable? What all parts do I need, or do you reccommend, for a DIY project, including any tools, tips, or tricks to make it go as smoothly as possible? Thanks for any help and by the way, your website is BY FAR, the best!
May 31, 2013
Followup from the Pelican Staff: Sounds to me like it could be the AOS. I would give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need. - Nick at Pelican Parts
Comments: I was driving home at around 50 mph, and had a smell of oil when I looked in the rear view mirrior the car was bellowing white smoke as I pulled over the CEL began to flash, I shut the engine down and had the car towed. Reading he CEL codes indicates misfire on cylinder 1, 2, 4. I have ordered the AOS and new plugs. Is there away of cleaning the oil contamination from the cylinder head before putting in new plugs and starting her up. Thanks for the artical it's been very helpful. The top PCV pipe was full of oil when I removed it.
May 15, 2013
Followup from the Pelican Staff: Cleaning the oil outof the engine is tough and messy. The only way to remove the excess oil is to remove the spark plugs, then crank the engine over. This does make a mess though. - Nick at Pelican Parts
Comments: OK I spent two hours last night and got everything disconnected except the clamp at the bottom, and so had to put everything back together. How on earth do you get that bottom clamp off? I could barely get my hand in there, let alone any sort of pliers to attempt getting it off?
Comments: First, thanks for making these tips and comments available they are life savers to say the least. I should have read through the comments section before I bought a replacement AOS from Pelican. I noticed one of the staff's replies indicated it would be a good idea to replace the PVC valve. I'd like to buy one from you guys but, I can't find it on your web site. Could you tell me what the P/N is for a 2000 Boxster S? Also, any other parts you can recommend? I don't want to blow another AOS because I didn't replace a cheap part. Thanks again for the help.
May 6, 2013
Followup from the Pelican Staff: Give our parts specialists a call. They will help you grab all the right parts: 888-280-7799 - Nick at Pelican Parts
Comments: 1997 boxster, purchased a new battery starts fine quickly dies.If after start up i pump the gas pedal continuously it stays barely alive when i stop depressing gas pedal shuts down.I noticed the oil level is above max could this cause problemsI read the oil oyxgen sensor could be the starting point.
Any advise would be appreciated.
May 3, 2013
Followup from the Pelican Staff: you could have a problem with your AOS. First check the DME for fault codes using a Porsche scan tool, correct the oil level issue, then inspect the AOS. - Nick at Pelican Parts
Comments: I bought my 2002 Boxster with 47k miles 3 yrs from a private sale. The day I picked it up, it blew white smoke for about 5 minutes then quit. The only persistent flaw I have had since purchase is a rattle in the rearmost catalytic converter on passenger side when in 1st or 2nd gear.
Last fall, the exhaust blew white smoke almost every other week. It had the other symptoms as well: rattling catalytic converter, CEL for rich fuel mixtures, fouled spark plugs, oil useage, louder than normal engine, and sluggish behavior.
I bought your book, and just started reading it front to back. I had never heard of the AOS until I read about it, and the problems it causes when it fails. I knew I needed to replace exhaust, but I decided to try AOS first. While waiting for it to arrive, I changed oil and filter, and cleaned my K&N air and cabin filters. After changing the AOS, I started the engine and it was noticeably quieter, and NO SMOKE! My Bentley book doesn't talk about the AOS, but yours does. I am so glad I bought it and read it, looking for projects to do, instead of looking for projects I knew I needed to do. I will clear CEL codes then I am confident I can drive it again while saving money for the exhaust overhaul. Unless you suggest something different.
As for the replacement, I took my time and patience, and it took two days: one to remove, one to install, each day about 1.5 hours. I spent about half my time under as above the engine.
Tip for squeezing the hose clamp off and on: Use needle nose Vise Grips to open it and hold it until you can slide it off. For install, while still on the workbench, I again used the needle nose Vise Grips, but after opening it, I placed a heavy duty zip tie on it to hold it open. I installed the AOS, slid the hose over tube after cleaning the tube, and using a dental mirror, I ensured the hose was snug, then clipped off the zip tie. I connected the other hoses, and finally screwed in the bolts. Cramped and crowded, but it still went just like your book showed. THANK YOU!
May 1, 2013
Followup from the Pelican Staff: Awesome, glad the article was helpful. - Nick at Pelican Parts
Comments: thanks can air/oil separator when is spoil and u block the pipe from intake.can it bring oil leakage in the engine i did that but engine oil leak to mush oleas let me know thanks
April 23, 2013
Followup from the Pelican Staff: Not 100% sure about what you are asking. BUT, if you are asking if thr air / oil separator can cause an oil leak into the engine, yes it can. If the diaphram ruptures, oil will be drawn into the engine. - Nick at Pelican Parts
Comments: How would I know for sure if I am to have the air-oil separator replaced? my 1997 boxster symptoms.The engine idle is poor irraticwants to shut down if I don't accelerateeven when I do it sometimes chokes.When cold I can hear a popping noise around the exhaust area.After I install a new battery could I do any additional damage by starting it up again.
April 23, 2013
Followup from the Pelican Staff: There is a test procedure for the AOS in the article you responded to. There are numerous items that can cause the symptoms you describe. The popping could be from improper fuel mixture or possible mechanical issues. If your battery is bad that can also cause running problems from low voltage. You will need to replace your battery and then properly diagnose your car.
- Denny at Pelican Parts
Comments: Hi Wayne.
I just completed the AOS replacement with parts from Pelican.
When my AOS went out, I was driving on the freeway with the top down. Before the smoke, I heard a strange whistle/whining sound, and then suddenly huge volumes of blueish smoke. I stopped and had the car towed, but not before driving almost a mile to find a safe place to stop.
Now the AOS is complete, it's blowing white smoke. At first, a LOT of white smoke, but after letting it run for 20min it's down quite a bit, but still puffs pretty hard when I rev the engine.
How long should the car be running before this smoking stops? Should I drive it or just let it burn off in the driveway. My biggest concern is that there's more wrong than just the AOS and I don't want to damage it further trying to burn off the smoke. Advice?
April 11, 2013
Followup from the Pelican Staff: Check your engine oil level, if it is good andn ot decreasing, run the engine until the smoke dissipates. There could be another problem, however if you have a lot of oil in your intake and exhaust system it may take some time to blow it out. - Nick at Pelican Parts
Comments: 2006 Boxster S 48K miles. 70 mph on cruise control, temp spikes puff of white smoke out exhaust. Slow to 50 mph, temp drops to 175, Pull off freeway into gas station, temp spikes again, oil pressure drops, car knocks. Turn off. oily water pours out bottom of passenger side of engine compartment. What say? Head gasket? Cracked head?. Hesitant to get it to a shop and have em drop the engine only to tell me it's shot and needs a replacement. Looking into some used Boxster engines online and the biggest company gets the worst ratings and some angry customers. Any suggestions on what I should do out there? I don't have home shop access so will have to trust a Porsche mechanic out here in Santa Rosa Calif. Car has been regularly serviced with no past problems. I'm devastated.
April 1, 2013
Followup from the Pelican Staff: Oil and coolant intermix could be a sign of a bad head gasket, as is the temp rising under load. I would have the cooling system pressure tested and see where the leak is. - Nick at Pelican Parts
Comments: Your figure #3 displays a Purple arrow to the second quick connect that travels under the Manifold to the other end of the camshaft to the left front of the engine,behind the driver seat. As I was removing the AOS from the topm it snapped. How is the best way for access in your opinion and also, I don't see a replacement vent line,only the short one.
March 16, 2013
Followup from the Pelican Staff: You may have to remove the intake manifold if you can't get to it from the top of the engine. It is a tight fit as it is, add your hands and even worse. - Nick at Pelican Parts
Comments: Pelican Parts is awesome! I had what appeared to be an AOS fail, but the mechanic insisted that it was an IMS fail and that the engine of my 2002 Boxster S was destroyed. I spent about five weeks looking into the options: scrapping the car, selling it to someone with an engine, finding a salvage Boxster and doing the swap myself, and even putting in a Suburu engine. Finally, I brought the car home while I waited for a good salvage engine to come on the market. Once home I decided to check out the OAS just in case the mechanic had made a mistake. Thanks to this article I was able to quickly determine that in fact it was the OAS that had failed! I took the car to another local Porsche garage and they confirmed that it was the OAS.
March 15, 2013
Followup from the Pelican Staff: WOW, awesome story. Thanks for sharing and glad it worked out for you. - Nick at Pelican Parts
I have just had a new head gasket fitted while it was being fitted a new AOS was fitted. When I ran the car the AOS blew when checked the engine had been overfilled with oil. 2 AOS later plus renewal of air intake pipes etc I got the car back. AOS has gone again what could be the issue 5k spent so far still no car. 2000 Boxter 2.7
January 20, 2013
Followup from the Pelican Staff: The air oil separator is a an emissions control unit whose purpose is to separate fuel vapors from the crankcase and funnel them back into the intake. These units fail over time when the diaphragm inside gets old and breaks. They can also be caused fail prematurely by other components on the engine failing, most noticeably the positive crankcase ventilation valve (PVC). If the ventilation valve is clogged or broken then the pressure / vacuum levels inside of the engine may become very high, and that puts a lot of stress on the air oil separator diaphragm. Typically when people have a air/oil separator failure problem, and it keeps happening again and again, it's often related to the PVC valve. I did a close look at this first. - Wayne at Pelican Parts
Comments: What is the crankcase ventilation valve Wayne mentioned in his response to Matt in October of 2011? What system is it associated with, and where is it located?
January 18, 2013
Followup from the Pelican Staff: The PVC valve (there are two of them) is attached to the top of the valve cover, and is also attached to the hoses that feed the air-oil separator. It may just look like a simple connector, but there's a valve in there. - Wayne at Pelican Parts
Comments: Removal Hint for the AOS. Great article and comments. My 2002 986 w/ 160k mi. had the usual symptoms CEL 1128/1130, smoke when started cold, rough idle until operating temp etc. Replaced the AOS from the top only with the aid of a disposable razor knife. Use the knife to slice or "saw" the bellows boot be certain your new AOS comes with a new boot at the base of the AOS of course exercise caution not the damage nearby wires or drop anything into the crankcase. Then remove the two vent lines a pair of needle-nose pliers may be necessary to gently coax them. An external E-10 socket was needed to remove the two bolts, although an 8mm socket fits surprisingly snug. Once the AOS is out of the vehicle, you can then remove the bottom clamp. Lastly, I replaced the bottom clamp with a standard hose clamp for ease of installation.
January 16, 2013
Followup from the Pelican Staff: Thanks for the tips! - Wayne at Pelican Parts
Comments: My AOS failed 100mi after I replaced it. In previous replies Wayne mentioned a crankcase check valve but there are at least three I know of. How do I find out which is it, please?
December 31, 2012
Followup from the Pelican Staff: The crankcase check valves are pretty cheap and easy to replace. I don't know the specific procedure for checking these, I would just replace all of them all at once and I think that would fix your problems. They are located on the top of the engine on either side of the valve covers. - Wayne at Pelican Parts
Comments: Idle on my 1998 boxter was going up and dawn so I replaced the hose and the oil separator,when I restarted the car the idle still going up and down so I opened the oil cap and this help some but still not perfect any help will be very appreciated. thank you
December 10, 2012
Followup from the Pelican Staff: Did you verify the separator was bad and leaking? There are a number of items that can cause an erratic idle. The idle surge is caused by a changing fuel mixture and you will need to find the cause.
Comments: I recently replaced the AOS on my 2002 986 with automatic transmission with parts from Pelican. Replaced it from top side. Not the easiest thing to do but be sure to get the quick release clamp. The job is a lot harder without it.
November 11, 2012
Followup from the Pelican Staff: Thank You for the tip.
Aloha from Hawaii
Comments: I took the oil filler cap off.A small amount of smoke was coming out of the filler even after the initial puff from the exhaust cleared up. Also there didn't seem to be excessive vacuum, but there was no change in the idle with the cap off.
My car puffs almost every morning on initial start and almost never again until the next morning. Should I replace the AOS ?
September 30, 2012
Followup from the Pelican Staff: I doubt that the air-oil separator is the problem. There might be some type of vacuum leak somewhere else, hence no change when you remove the oil cap. But if the AOS was failing, then you would have a lot of vacuum pull at the oil cap (most likely). - Wayne at Pelican Parts
Comments: My 2002 70k boxster's oil/air seperator failed on the weekends, huge clouds of thick white smoke billowing out of the back. Only bought the car two months ago, from a prviate seller, so was pretty nervous I'd bought a dud when the smoke started.
Took it to Vertex Automotive in Miami who changed the part out for $680. Not cheap but am just glad its fixed. Thanks to Pelican for all the detail on this site, was really helpful and am now going to try and change air and cabin filters myself!
September 27, 2012
Followup from the Pelican Staff: Thank you for your comments. Changing those cabin filters is easy compared to the separator.
Comments: What is average cost to replace the oil seperator and replace valuce in Cyl #1?
September 19, 2012
Followup from the Pelican Staff: Labor rates vary wildly by the location and type of repair facility you use. If you are going to use a shop for the replacement I would get quotes from a few local shops that work on Porsche's as a speciality. They will be most familiar with your Boxster and have the proper tools and equiptment.
Comments: I was driving my 2007 boxter home from the mechanic when it made a gurgling noise and the check engine light went on. When I arrived at home and parked it all of the oil ran out of it. What is wrong?
June 20, 2012
Followup from the Pelican Staff: I am sorry to hear that. I would contact the shop and have them tow it in for inspection. Do not start the engine or drive your car until the cause of your oil loss is determined and repaired.
Comments: Thanks for the great instructions on replacing the Oil Air Separator. I cut mine apart after removing it, and here are the photos of the diaphragm with at least three small tears in it.
June 15, 2012
Followup from the Pelican Staff: Thank You for your comments and the picture. That is the typical internal failure the the AOS.
Comments: changed my separator about 100 miles ago on a 3.2 s boxster 2002 no smoke but still running lumpy and holding back do i just keep driving it and hope it clears or try something else??
May 31, 2012
Followup from the Pelican Staff: Did you verify the AOS was leaking prior to replacement? Other causes could be fouled Oxygen sensors caused from the oil from the leaking separator. Also air mass sensors can cause poor running and surges in power.
Denny at Pelicanparts
Comments: Wayne - I recently purchased a 1-owner '02 Boxster w/55K miles & a clean CarFax. Dealer previously did 60K service at 46K & replaced clutch. We had a local shop do a major service & inspection upon purchase with exception of air filter due to availability.
At 57K, CEL with no exhaust smoke showing Codes P1128, P1130 - replaced air filter; cleared codes.
Short ride, CEL with same codes - cleaned MAF w/CRC; cleared codes.
Another short ride, CEL w/same codes & irratic idle 650-800, high vacuum at dip stick & unable to remove oil fill cap - replaced Oil Separator & cleared codes. Oil was present in the tube leading to the intake manifold.
Engine idle now steady 700 rpm, low vacuum at dip stick & able to remove oil fill cap w/engine running. Test drove 22 miles with no smoke & steady idle 700 rpm. - no CEL.
Parked car in garage & noticed small oil leak on the ground about 5" circle - oil leak appears at bottom of bell housing/engine mating. NO engine leak noted before replacing Oil Separator. Cleaned up concrete & no fresh leak noted.
What do you think would cause this? Rear Main Seal??
Thanks for your 101 Project book & website - have been a wealth of information in diagnosing this issue step-by-step.
Would greatly appreciate any insight/expertise you can provide to point me in the next direction to get the problem resolved.
Thanks - Rich
May 14, 2012
Followup from the Pelican Staff: It does sound like the problem was with the air-oil separator, in that you could not remove the oil cap with the engine running. That is a clear sign / clue. When there is very high crankcase vacuum, the engine tends to draw in air from the seals too, which can actually damage them. It may be that the rear main seal is damaged, but I would just drive the car for a bit and see if the oil leak continues. It may be that the seal reseats itself after being pulled around by the crankcase vacuum. - Wayne at Pelican Parts
Comments: Anyone know if the 944 AOS unit has check valves or a control diaphragm in it? Spring and rubber diaphragm that control the flow rate into the cyclone
May 11, 2012
Followup from the Pelican Staff: Hmm, I've actually never heard of the 944 having one of these air-oil separators. It's actually a newish type of emissions control device. - Wayne at Pelican Parts
Comments: Some of the talking heads on several of the Boxster/Cayman owner forum sites e.g. Planet-9 and the CaymanRegiter.org, and others have suggested replacing stock air oil separators with I gather, but have not seen one to compare a larger and more robust Porsche Motorsports AOS. Does Pelican have a position on this, and does it have or stock the Motorsport AOS part?
May 10, 2012
Followup from the Pelican Staff: Michael,
Wayne started a thread on this topic last year. See it here:
- Scott at Pelican Parts
Comments: I have a 2000 Boxster with 105K on it. I'm the original owner. Just repleaced the AOS over the weekend. I found it best to remove the nut holding the coupling for one of the O2 sensors from underneath. You have to unplug the senor to get to the 10MM nut. You need to press in on the coupling tab at the bottom to release the plug. Also the two vacumn lines that attach to the AOS One from above and the other one best serviced from belowis difficult to remove. I used a small flat head screwdriver as a small pry bar take care not to warp the plastic to separtate the AOS from the vacum fitting. All-in-all, I took my time and all went according to the diagrams and discussions above. I have a Porsche Service Manual by Bentley publications, and it did not even mention the AOS. This techincal was a game changers. THANKS!!!!
May 7, 2012
Followup from the Pelican Staff: Thanks for the kind words and the good tips! - Wayne at Pelican Parts
Comments: I have a 2001 boxster with 80,000 miles in it.during a drive comming from Vegas i notice a cloud of white smoke comming from the exhaust pipe. i was able to leap home without busting my engine. I also suspected that something was wrong with the air/oil separator. I am going to bring my car to the dealer. How much do you think will i spend for the replacement of the separator? Thanks.
April 26, 2012
Followup from the Pelican Staff: Labor rates vary wildly. I would recommend getting several quotes on replacement from a dealer and some local independent shops that specialize in Porsche's.
Denny at Pelican Parts
Comments: I have a 2005 Boxster with 52k miles. The car has a "small" leak around the area where the Air/Oil separator is located. I don't have any of the problems mentioned in the threads above, but i'm kind of curious if it is not the Air/Oil separator, what else could it be that is causing it to have this area somewhat oily/dusty top right rear corner of the engine.
April 19, 2012
Followup from the Pelican Staff: Even if the separator has not failed there is oil and vapor in the hoses and AOS system. I would recommend cleaning the area, checking the hoses and clamps and going of a drive. After your drive recheck for any leakage.
Denny at Pelican Parts
when i remove the oil filler cap on my 2.5 boxster there is a loud noise of air blowing out of the filler, i have also lots of oil on top of my engine under the right handside air intake,the oil separator conections seem dry,is it possible that the oil is coming from the crankcase connector,removed oil separator,all pretty gunged up.Cheers for any help.
March 17, 2012
Followup from the Pelican Staff: I wouild recommend replacing the AOS as they are a common failure item that cause the problems you describe. After replacement clean the top or your engine go for a drive and then recheck for leaks.
Denny at Pelican Parts
Comments: Great help that was , first i thought the rings or the valve seals gone bad. changed the oil separator at a cost off $385
including the oil change parts an labor , and that took care
the heavy smoke the boxter is back to normal.
March 9, 2012
Followup from the Pelican Staff: Alway happy to hear success stories. Thank You for your commments.
Denny at Pelican Parts
I have a 99 Boxster and I need to replace the oil separator ASAP because of bad performance and a popping noise when the car is cold. However, Where do I find the updated connecting house mentioned?
"If you are replacing your air-oil separator with a new one, be sure to install the updated connecting hose as well."
March 7, 2012
Followup from the Pelican Staff: Pelican Parts can supply the hose you need.
Denny at Pelican Parts
My 98 boxster just turned 64K and I started hearing an intermittent chirping noise that I think is the oil/air separator going bad, everything I've read indicates a squelling noise, sny suggestions about how to confirm.
March 2, 2012
Followup from the Pelican Staff: There is a diagnostic procedure in the AOS replacement article that requires checking crankcase vacuum. You can test your AOS using that procedure. With your stated mileage it would be a good idea to replace yous even if it has not failed yet.
Denny at Pelican Parts
Comments: I kind of feel "conned" by the pictures in Wayne's book and in the tech article on replacing the air / oil separator. I have a 2001 Tiptronic Boxster and there is literally no way to get at the separator from underneath the car. It took me 10 minutes to be able to even see it! My mechanic last time said he would remove the engine to make the replacement and I thought from long experience with VWs that he was probably doing it for convenience not necessity.
The tech article and book ought to note that there is a world of difference in the structure under the car with the Tiptronic and this is not a DIY project for the home garage...
February 24, 2012
Followup from the Pelican Staff: Yes it's difficult to get to the AOS from underneath the car with the automatic transmission installed. However, you can indeed replace it from the top of the car - it's just a little bit more difficult. - Wayne at Pelican Parts
Comments: Be careful removing the unit. The flexible plastic tube connecting to the intake on the top of the separator can be very brittle from the engine heat over the years. Mine broke clear through almost as soon as I removed the clip to the separator. If you're reading this now before ordering parts, it may not be a bad idea to order this tube. I wish I had.
February 11, 2012
Followup from the Pelican Staff: Thank You for your comments. I recommend replacing the hoses and tube when replacing the valve. Oil, Oil vapor and age does make these items brittle over time.
Denny at Pelican Parts
Comments: I just got this done and it made quite a difference. Before I use to get large amounts of smoke at start up and a nonstop amount of smoke after the car was warmed up. I had O2 sensor failures and misfiring engine codes. Its been a week now and had not had anymore of those issues. It was quite a a task though.
One problem I have is that I damaged the thread of the hole where it mounts to. Does anyone know what threaded insert threaded need as well as the pitch on the thread? I measured the outside diameter of the screw thread and it was .233" which is about 6mm, and that's all I know any help is well appreciated it.
February 7, 2012
Followup from the Pelican Staff: It is a 6MM X 1.0 thread. I would recommed trying to retap the threads first. If that does not secure the bolt you will have to use a threaded insert or helicoil for repair.
Denny at Pelican Parts
Comments: Removing the hose purple arrow can be a pain as there are so many obstructions. Best way is to disconnect the two bolts that attach the AOS to the engine and also the bellow at the bottom. This will allow you to lift up the AOS from the top and give you enough room to squeeze the clamp and remove the hose. I also followed recommendations to replace the hose clamp for the bellow and the J tube to a screw type. Much easier to work with.
January 14, 2012
Followup from the Pelican Staff: Thank You for your comments.
Denny at Pelican Parts
Comments: Greetings Wayne.
I have just experienced this problem with a 2001 boxster. Excessive smoke and CEL. shut down as soon as light came on and now engine will not turn over. Could the engine have ingested too much oil and just be hydraulic locked or or do you think it could be worse? Thanks
January 6, 2012
Followup from the Pelican Staff: If too much oil entered the combustion chambers it could cause your engine not to turn over. I would recommend removing your spark plugs and then try turning the engine a few revolutions. It it does not rotate then your problems are deeper than a failed AOS.
Denny at Pelican Parts
Comments: Do you have any info on the air oil separator in an 2007 997 3.8L car, i have one that has 10"hg vacuum at the oil cap, huge amounts of smoke on sartup
January 4, 2012
Followup from the Pelican Staff: The AOS has similar problems to the earlier models. Give our parts specialists a call, they will help you find the right parts: 888-280-7799 - Nick at Pelican Parts
Comments: Great info...wish i had read this before i took it into my porsche shop $$$. but now i am getting a light smoke that comes out of the passenger side air intake area that leaves a black residue. i have had something similar happen when my water pump went out and it melted some belt. could this be the same issue? any ideas or help before i take it into my shop?
January 3, 2012
Followup from the Pelican Staff: I suspect the smoke is caused by an oil or water leak. The black residue could be from another belt or drive failure. I would diagnose and repair what ever the cause is ASAP.
Denny at Pelican Parts
Comments: Thanks for this thread Wayne. Very good stuff and saved me a bunch 'o money.
One more question. I read that 100 - 200 miles of driving should help burn off all the unwanted oil in the intake/motor/exhaust. I'd really like to help this along 'cause the exhaust still stinks especially after it's been warmed up. Could you recommend a fuel additive to help remove all the gunk that will be safe to use in my precious Porsche? Thanks.
January 1, 2012
Followup from the Pelican Staff: The stuff that you need to burn off is in the intake. Other than disassembling the entire intake and cleaning it out, I don't see a shortcut on this one. - Wayne at Pelican Parts
Comments: Going through a corner hard on the gas and pulling a lot of G's I noticed a large cloud of blue smoke was following me and although during wartime that can be used as cover, but probably not a standard Porsche design. Is that likely to be a bad air/oil separator? Little or no vacumn detected when removing the oil filler cap, with engine running.
December 3, 2011
Followup from the Pelican Staff: This could be a sign of a failing air-oil separator, or it could just be normal operation for a street component (the separator). Porsche has a separate motorsports air-oil separator that they supply that is used in on-track cars where the G-forces will be higher. If you're going to be driving your car hard, then you might want to look into installing one of these. - Wayne at Pelican Parts
Comments: I have an original AOS still installed with no problems, car has 70k on it should I replace it? Or is it good to go?
November 30, 2011
Followup from the Pelican Staff: If you're not experiencing any of the known issues with the unit (high vacuum, smoking, etc.), then I wouldn't worry about it until it fails. - Wayne at Pelican Parts
Comments: I have 1999 boxster monday the engine light came on and the car died.I had it towed home and it will start, but it will
not run properly. It makes loud noises, Have any idea.
It's been running perfect for around 14 months. No warning at
all. No oil leaks.
November 2, 2011
Followup from the Pelican Staff: You need to check the fuel injection trouble codes using a code reader. Check out our article on the subject (in the tech articles section). Without knowing this information, you're just guessing blindly. - Wayne at Pelican Parts
Comments: When you replace the AOS, do you recommend replacing the o ring on the bottom right angled connection into the right side of the engine? part number 996 107 122 00.
Also, I changed my AOS a few months ago, but i am again getting smoke on start up. I disconnected the line from the AOS to the intake & found oil. Could the new AOS be faulty, have there been a bad batch or is it some other problem in my car?
October 5, 2011
Followup from the Pelican Staff: Sure, it's a smart idea to replace the o-rings on all of the connections that you've disturbed. If there is a big vacuum pull from your engine, it will cause air oil separator units to fail prematurely. Too much vacuum can be caused by a broken / stuck crankcase ventilation valve. I would check that it's not pulling too much vacuum on your engine. - Wayne at Pelican Parts
Comments: Does anyone know the part number for the plastic tube that connects to the bottom of the AOS? It's the tube with the purple arrow pointing to it in figure 3.
September 8, 2011
Followup from the Pelican Staff: On the Boxster 986, this bellows is part number 996-107-237-52. - Wayne at Pelican Parts
Comments: Hi, today coming from work my 01 Boxster non S started smoking real bad I stopped the car right away and towed it home cause I knew the AOS went bad. But when I got home and started it up I heard a bad noise in the engine. Is there something else wrong with the engine? Should I go ahead and replace the AOS and pray and start it up? Pleas help me out I just retired from the NAVY and dont need this right now
August 22, 2011
Followup from the Pelican Staff: Okay, don't panic. When the air-oil separator fails, it pulls a huge vacuum on the engine, when then can cause odd noises to happen. Most common is a whistling noise as air is drawn into the engine past slightly leaky seals. Odd behavior. Here's what you can do to test - remove the small hose that connects the AOS and the throttle body and plug both ends. Then run the engine and see if the noise is still there. If yes, then you probably have other problems. If no, then it's probably the AOS. Only run the engine for a short time in this configuration, as the piston rings work best and expect the engine crankcase vacuum to be at a significant level when running. - Wayne at Pelican Parts
Comments: I'm confused... I searched Pelican Parts for an AOS for my 2002 Boxster S and ordered part #996-107-080-54-OEM based upon he search results. I also ordered you 101 projects book. In the book it mentions that I may need a new hose as the existing one may be to short. So I came to the project site to see if it had a parts list to find the correct hose part. The project list says I should order part #996-107-023-04-M100. Both parts are listed as Genuine Porsche parts for an AOS for a 02 Boxster S. Can you help? Do I have the right part? Do I need any additional parts?
Thank you for any assistance you can provide!
August 16, 2011
Followup from the Pelican Staff: Give our parts specialists a call: 888-280-7799 They will help sort the part numbers. - Nick at Pelican Parts
Comments: My car is smokin!!! White smoke pouring out of it for the first 10 minutes. When I open the oil cap there is a vacuum. There is old oil all around the AOS
Can you do damage driving like that and should you replace the J Tube with the AOS?
July 27, 2011
Followup from the Pelican Staff: It's not good for the catalytic converters to be subjected to oil like that. In general, you won't do too much permanent harm if you only drive it for a little bit. But, I would get it replaced as soon as possible. If you're talking about the tube that connects the AOS to the throttle body, see if yours fits first and then get the updated one if you need it. - Wayne at Pelican Parts
Comments: everytime i start my boxster from a cold start i hear a clinging metal rattling sound near the exhaust system i hear the sound only when starting but not when running, and when it heats up and i start again, its gone. my mechanic said change the oil separator, what do you think guys?
July 10, 2011
Followup from the Pelican Staff: It's nearly impossible to diagnose problems like these over the Internet, but if I were to take a wild guess, I would say that there's something loose in the exhaust that is causing the rattle. Probably pretty minor, but it is annoying though. I have an exhaust rattle in my Boxster right now - I think it's one of the heat shields. When the car is cold you might want to get under there and literally poke around with your hands to see if you can feel if any of the shields or pipes are loose. - Wayne at Pelican Parts
Comments: I just replaced the AOS however, it still bellows a huge amount of smoke and the rough idle. Can you give me some suggestions?
Update, thank you for the great DYI info. After replacing the AOS I started the car while still on the jack. My 16 yr old son said that maybe if it is a flat 6 and on the angle of the jack the oil is in the pistons. Bingo! He has been begging me to teach him how to drive the porsche and I think he just earned his ride.
July 9, 2011
Followup from the Pelican Staff: Yes, that will happen perhaps. More likely is that the oil is still saturated inside of the intake and will need a few miles to "blow itself out." It's very common to have significant amounts of smoke upon startup after replacing the air-oil separator on the top of the engine. - Wayne at Pelican Parts
Comments: Hi... I track my 2002 Boxster S quite a bit and am regularly getting the plumes of smoke. The solution seems to be the performance aos. My mechanic got one for me to find out that the mounts are different. We learned that the design changed in the 2003 my. Now we're trying to figure out how to make it work. Any suggestions? Thanks very much.
June 23, 2011
Followup from the Pelican Staff: I'm not sure, as I'm not aware of a change in the motorsports unit that doesn't allow it to mount properly. I'll copy this question to the forums, where a bunch of people have done this upgrade. Perhaps they will have some suggestions for you. - Wayne at Pelican Parts
Do you have any images of the other end of the line to the crankcase? Where does it attach? Is there a vent line associated with this line has a spring inside it near the crankcase attachment?
Sorry, disregard the image request, I found one in your online parts catalogue 996-107-047-51-M100. I am trying to work out how this part, with a small vent? port works.
Cheers, great site & forums!
April 15, 2011
Followup from the Pelican Staff: Hi there. I'm not sure I completely understand the question - I will copy this to the forums where we can discuss it there... - Wayne at Pelican Parts
Comments: hi my 2000 boxster says 996 on the engine case is this the right one?
March 6, 2011
Followup from the Pelican Staff: Yes, the Boxster was developed in conjunction with the "new" 911 at the time (the 996), and as such, they share a tremendous number of technologies and parts. It's very common to see part numbers starting with "996" on Boxster parts. - Wayne at Pelican Parts
Comments: I just replaced my oil separator on my 2005 Boxster last week according to your instructions thanks much. But a few days later I noticed the Check Engine Light came on and stays on even though everything seems to be running fine and no unusual sounds are present. Does it just need to be reset or could there be a related issue?
February 21, 2011
Followup from the Pelican Staff: It could be one of two things that I can think of off the top of my head. Firstly, the oil that came out of the air-oil separator may have been sucked into the intake and has gummed up the intake and possibly the MAF sensor. I would check out my tech article on this and clean it out and/or possibly replace it if it's covered in a thin film of oil. Secondly, if the air-oil separator is not installed properly, then you may have a vacuum leak, which could potentially cause some codes to trip. You need to figure out what code is triggering - you can do that with a code reader - see my article on reading codes too: http://www.pelicanparts.com/techarticles/Boxster_Tech/20-FUEL-Code_Reading/20-FUEL-Code_Reading.htm - Wayne at Pelican Parts
Comments: I have replaced two air oil separators on my 2001 Boxster in 71k miles. The second one lasted 4 years and 20k miles. It displayed the typical rough idle/smoke at start up/ CEL light. I have the defective separator on my bench and air move freely through it from all ports. What component inside goes bad? My mechanic says my short infrequent trips and long 5000 mile interval oil changes are to blame
February 19, 2011
Followup from the Pelican Staff: I haven't taken one of these apart yet, but I suppose that I should to better understand exactly how they work. The purpose of the device is to pull vapors using the vacuum of the intake, without pulling the oil from the sump into the intake. When they fail, the oil gets sucked into the intake, and you can feel a big vacuum draw on the oil cap when you try to remove it with the engine running. I believe that there is a diaphragm of some type in the device (like a filter) that sucks air but blocks oil. - Wayne at Pelican Parts
Comments: the test done with motor runing could not remove oil filler cap,huge amount vacume, may i loosen or remove oil filler cap to drive car to dealer 50 kms away or must i have boxster towed to dealer.
Comments: I've just had my air-oil seperator replaced - unfortunately this was after the massive cloud of smoke.
My local garage here in the UK have run compression tests to confirm that the engine is still okay. But even after switching in a new air mass meter the car is very much down on power and hestitating - they've advised me to run the car for a while and see if it'll burn off the oil that most likely is corrupting the readings on the exhaust sensors and or catalytic converters.
My question is, is this a possiblity or should i be prepared to have to replace those parts?
January 11, 2011
Followup from the Pelican Staff: Yes, you should run the car for about 100-200 miles and re-evaluate. It will take time to burn all of that crap out of there. You might want to clean out the throttle body too to help it along. After that, it *should* come back to normal. - Wayne at Pelican Parts
Comments: When I cleaned my Throttle Body the air-oil seperator looked clean and in good shape. I tried the 'remove the oil cap test' with my hand and there is a vacuum, it's not super strong but definitely there. The idle goes up when I do that, I assume that is normal. The reason I ask all this is I was reading where I thought someone said there should be no vacuum which seemed odd to me. I guess I can try it on the Benz.
December 24, 2010
Followup from the Pelican Staff: Yes, it is perfectly normal to have some crankcase vacuum in the engine. When you remove the oil cap in the rear trunk of the car, the engine idle should dip down a bit - it will not run properly with the oil cap removed, or a leak on the oil cap seal. Sounds like what you have here is 100% typical and normal. - Wayne at Pelican Parts
In the second paragraph up from the bottom gray boxes it says ...intake maifold yellow arrow, Figure 1....
It should be figure 2 since that is where the yellow arrow points to the intake hose.
Just want to help.
Waiting for the book.
October 21, 2010
Followup from the Pelican Staff: Cool, thanks. The book comes out next month! (December 2010) - Wayne at Pelican Parts
Check out some other sample projects
from the book: