Pelican Technical Article: Air / Oil Separator Wayne R. Dempsey
Time: 2 hrs
Tab: $110
Talent:
Tools:
-
Applicable Models:
986 Boxster (1997-04) 987 Boxster (2005-08)
Parts Required:
New air-oil separator
Hot Tip:
Check the oil cap for an unusual amount of crankcase vacuum
Performance Gain:
No more oil screen behind you
Complementary Modification:
Change the oil
This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster. The book 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 for more details.
Check out some other sample projects from the book:
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.
Figure 1
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: 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
Elanman
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
Michael P
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:
http://forums.pelicanparts.com/boxster-cayman-forum/606549-motorsports-air-oil-separator.html
- Scott at Pelican Parts
Jim K
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
JR
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
Jsalcedo
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
mally
Comments: hiya 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
sam
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
perla
Comments: Hi,
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."
Thank you
March 7, 2012
beeper71IR
Comments: Wayne, 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
Chris
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
Chris
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
jolujaper
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
bala
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
grizzlyalan
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
pdafoe
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
richth96
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
ptracer
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
Kimberboy
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
Harry Kamaltow
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?
Thanks HK
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
franco
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
matt
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
Carlos
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
Angel
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
Colin
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
Ricey
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
paolo g
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
Jim
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
MIB24
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
matt
Comments: G'day,
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
kris
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
Moe
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
aahighfly
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
ant
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.
February 10, 2011
Followup from the Pelican Staff: Yup, that's a classic air-oil separator issue. You should be okay to drive the car to the dealer, I would just keep the rpms low, and drive cautiously. The failure of the separator means that the engine may be sucking oil into the intake. You might want to have them change out the spark plugs too while the car is there. Or, you can simply perform the replacement yourself using my handy article: http://www.pelicanparts.com/techarticles/Boxster_Tech/09-ENGINE-Air_Oil_Separator/09-ENGINE-Air_Oil_Separator.htm - Wayne at Pelican Parts
Longstar
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
Hal
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
RickE
Comments: Hi,
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:
