Make sure that you have a 4 quart drip pan and plenty of paper towels
Longer life transmission
Use Swepco 201 transmission fluid for better shifting
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101 Performance Projects for Your Porsche Boxster. The book
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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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Check out some other sample projects
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One of the easiest tasks to perform on your manual transmission Boxster is to change the transmission oil. The Boxster transmission is what is known as a transaxle. It includes all the standard components of a normal transmission, plus an integrated differential. This design is possible because of the mid-engine design of the Boxster. The transaxle design is more compact and theoretically lighter in weight since you don't need a dedicated differential.
The differential and the transmission both share the same lubricating fluid. It's very important to make sure that the fluid in your transmission is at the proper level, otherwise your transmission will experience significant wear. The synchro rings and sliders all depend on a slick surface in order to match speeds when shifting. If your transmission is low on oil, the wear on these components will accelerate significantly. In addition, shifting the car will be more difficult. One of the first things that you should check on a Boxster that is having problems shifting is the level of the transmission oil. Keeping the differential and all the associated gears well lubricated should also help increase your fuel mileage.
The transmission oil also helps to keep temperatures down inside your transmission. The engine is one of the primary sources of heat for the transmission as it conducts and radiates through and around the points where the engine and transmission are mounted. The transmission also creates heat itself as the gears and synchros turn within its case. Keeping the transmission fluid at its proper level helps to mitigate heat problems. Having a large reservoir of oil to spread the heat throughout the transmission helps to keep temperatures down. On some of the higher performance Porsche transmissions, there is even an external transmission cooler that operates similar to the engine cooler.
I recommend that your transmission fluid should be changed every 30,000 miles or about once every two years. This number is a rough estimate, and may vary depending upon your use of your Boxster (track vs. street). There are many moving parts in the transmission, and they have a tendency to drop small microscopic metal particles into the oil. Specifically, the synchro rings wear down slowly over time, each time you shift. While the transmission bearings are not as sensitive to oil contaminants as the engine bearings, they can still exhibit wear from these particles in the oil.
The Boxster transmissions have two plugs for filling and emptying the transmission oil, located on the side and the bottom of the case. The five-speed transmission requires a 17mm hex socket to remove the filler plug, and a 16mm triple-square anti-tamper socket (Hazet 2567-16) to drain the fluid. Both are available in the online catalog at PelicanParts.com. The six-speed plugs are a bit more generic: a 10mm hex socket is all that is required to remove both the drain plug and the filler plug.
If you are simply checking the level of oil in your transmission, start by removing the filler plug on the side of the transmission. This is the plug that you add fluid to. For the five-speed transmission, take a large paper clip bent it at a right-angle, stick it inside the hole pointing towards the ground, and measure the fluid level on the paper clip. This mini dipstick should register transmission fluid at about 11mm below the lowest edge of the filler hole. Make sure you do this when the car is cold, and parked on level ground. If the level is lower than 11mm, then you will need to add some fluid. For the six-speed transmissions, it's a bit easier. Simply stick your finger in the hole and see if you can feel fluid at the bottom level of the hole. If you can feel the fluid level with your finger, then your fluid level is about right, or perhaps will need only a little topping off.
If you cannot feel the fluid level, then you will need to add transmission oil to the case. If you are planning on changing the oil, then remove the plug on the bottom of the transmission case. It's a wise idea to try to empty the transmission oil when the car is warm, as this will make the oil more viscous and it will flow out easier. Make sure that you have a drain pan capable of handling at least 4 quarts of transmission oil. Check the fluid in the pan to see if you see any unusual metal pieces, or grit in the oil. The five-speed transmission holds about 2.25 liters (2.4 quarts), and the six-speed transmission holds 2.8 liters (3.0 quarts).
While the fluid is emptying out, you can use this time to clean out the drain and filler plugs. The bottom drain plug should have an integrated magnet in it that traps metal debris. Using a cotton swab or a paper towel, carefully clean out all of the black debris and particles that may have found their way in there.
Replace the bottom plug on the transmission, but don't tighten it too tightly (18 ft-lbs or 25 Nm maximum). These plugs do not have a tendency to leak (transmission oil is thicker than engine oil). If it does leak later on, you can always tighten it a little more. Now, add transmission oil to the case. The best method of doing this is with a hand operated oil pump. These are available from most auto parts stores and attach to the top of the plastic transmission oil bottle. They work very similar to the liquid soap dispensers you find in most bathrooms. Pump the transmission case full of fluid until it just starts to run out the filler hole. Replace the filler plug and clean up the few drips that might have run out of the hole. Tighten down the filler plug in a similar manner to the drain plug.
The automatic transmission cars also have a differential built-in to the transaxle. This differential uses the same type of fluid as the manual transmission and must be checked and filled in addition to the automatic transmission fluid. On the automatic cars, there is no drain plug however, so the gear oil must be drained by loosening the outer differential cover (see Project 39 and Figure 5). Or, you can possibly get around this by inserting a fluid vacuum pump into the fluid fill hole and sucking out all of the old fluid. You top off the fluid and fill the differential in a similar manner to the six-speed transmission. Simply unscrew the plug and fill until the fluid starts flowing out of the hole. The automatic transmission uses the same fluid as the manual transmissions and takes about 0.8 liter (0.85 quart). Tighten up the drain plug to 22 ft-lb (30 Nm).
In many cases, generic transmission gear oil that meets or exceeds SAE 75W90 will suffice perfectly fine. Also very effective are the Porsche factory lubricants (typically manufactured by Shell Oil), or Mobil Delvac Synthetic Gear Oil 75W-90. Although technically different from the original Porsche gear lube specifications, I've run Swepco 201 in my Boxster transmission with very good results. In addition, if you have a Limited Slip Differential (LSD), be sure that you get transmission fluid that is appropriate: using a fluid that is too slippery can reduce the torque bias effects of the differential and make it less effective at distributing torque.
This photo shows a typical 5-speed Boxster transmission that has been removed from the car. You need a special hex socket in order to remove the filler plug located on the side (17mm for the 5-speed and 10mm for the 6-speed). The inset photo shows the 17mm hex socket tool along with the special 16mm triple-square anti-tamper drain plug removal tool required for the 5-speed transmission. The 6-speed requires only a 10mm hex socket. The lower inset photo shows the transmission being filled using a hand pump.
Here's a photo of the five speed transmission from my Boxster being reinstalled. With all of the exhaust components out of the way, it shows a clear view of where the drain plug is located in relation to the rest of the transmission (yellow arrow). The inset photo shows a close-up of the wacky plug that requires the triple-square removal tool. I'm not sure what the motivation was for Porsche to use such a specialized plug here.
The five-speed transmission should be filled approximately 11mm below the bottom edge of the fill plug in the side of the transmission. Use a paperclip as a mini-dipstick to measure the level inside the transmission, as shown here in this diagram.
Shown here is the side of the automatic, Tiptronic transmission for the Boxster. The green arrows point to the differential cover bolts that need to be removed in order to loosen the cover and drain the differential gear oil. If you can't empty the differential by simply loosening the cover bolts, then you need to remove the center bolt and pull out the stub axle. The red arrow points to the fill plug. Top off the fluid to the edge of the bottom of the fill plug, just like on the six-speed transmission.
Comments: Hi, i own a 2003 Boxster S with a G86.20 6 speed MT. Changed the transmission oil on a hydraulic leveled ramp. Didn't check the volume while draining. Put 2.9 liters in, but the oil didn't overrun. Tested oil level with finger, but it was still below the hole where you fill in the oil. So i'm wondering if this transmission needs more transmission oil. Thanks
June 20, 2014
Followup from the Pelican Staff: 3 should be enough if you just drained and filled. However, I would recommend topping up until you are at the correct level. It's even worth getting it right, then rechecking after driving. - Nick at Pelican Parts
Comments: My car is on a lift as it has been stored for winter since December. Would you still recommend changing the oil with the tranny warm or is there value to doing so in its current state as ALL of the oil has certainly dripped off of higher components and is in the bottom of the unit. AKA: Is it worth splitting hairs in this case to have the tranny warm? Thanks!
March 29, 2014
Followup from the Pelican Staff: You should be Ok keeping it cool. Warming it allows the fluid to drain down, and drain faster. If yours has been sitting, I don't see the need. - Nick at Pelican Parts
Comments: I have a 1998 Porsche 986 Boxster with tiptronic 5 speeds transmission. Recently started to leak in the right side. The oil seems to come out somewhere through the shaft flange. I believe a seal is damaged but don't know which one and how to change it. Can you help me with this pls.
March 22, 2014
Followup from the Pelican Staff: Could be the stub axle seal in the gearbox. You will have to remove the axle, then the stub axle. Then replace the seal. - Nick at Pelican Parts
Comments: 1. I have just bought a 2002 manual 5 speed Boxster. It would be easier to change the transmission oil if the alloy cover under the transmission had a 2 inch hole drilled through it directly under the plug. Is there any reason why this should not be done?
2. The drain plug is off to one side of the transmission. If it can be done, does anyone have exact measurements for the location of the centre of the drain plug in relation to the centre of the transmission, or better still the edges of the plate laterally and longitudinally, or even better still, lat and long in relation to the existing small 3/8 inch drip hole in the entre of the alloy plate?
3. If this idea is feasible and doesn't compromise the car in any way, it would save owners and garages a lot of time. The 2 inch drilled hole could be filled with a rubber or plastic plug between oil changes. It seems so obvious there MUST be a reason the Porsche engineers didn't design an oil change hole in the plate themselves. If it is feasible, I suggest the transmission drain hole could be documented as one of your minor projects.
3. Congratulations to the Pelican web site creator and developers. It is a great source of information.
January 29, 2014
Followup from the Pelican Staff: The pan is for structural support, do not modify it. - Nick at Pelican Parts
Comments: Did this today. Used the Swepco 201 tranny fluid.
-My tranny cover was very easy to remove. As was both drain and fill plugs.
-I made a total mess with the extension tube on the piston filler launching itself off. Had to hold that in place while pumping the new tranny fluid it.
-first few shifts after the change were scary...I mean scary bad...but 3-4 blocks down the road and everything was great. Much better shifts and generally smoother all around. Very happy now with this project as it has fixed my 1st to 2nd sketchiness I've been having.
December 12, 2013
Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
Comments: Mine is a 2002. It would be helpful to hear if any that old had LS. Thanks.
June 19, 2013
Followup from the Pelican Staff: I believe in 2002 Boxster models were available with PSM traction control, which was described at LSD in the option code. However, I also remember it not being a true LSD. You can always install one yourself. - Nick at Pelican Parts
Comments: Is the differential Limited Slip? Would Mobil1 75W90 LS be a good fluid? Thanks for the helpful articles!
June 18, 2013
Followup from the Pelican Staff: A limited slip was optional in Boxster models. Give our parts specialists a call, they will help you choose the right oil. - Nick at Pelican Parts
Comments: I'm looking at wayne's "correct" photo of the fillplug for the 6-speed. Something seems wrong:
1. either the photo is reversed, or
2. it suddenly on the passenger side again, or
3. this is a 996 and the tranny is reversed
Can you clarify?
April 20, 2013
Followup from the Pelican Staff: Sorry for the confusion, the photos only show the 5-speed transmission. - Wayne at Pelican Parts
Comments: For clarity, the reason the 5-sp is different in fill level, fill hole location etc is that it is in fact an Audi 01E transmission, not a porsche unit at all. From what i can tell, this is a *good* thing.
It requires the M16H triple square security socket.
April 20, 2013
Followup from the Pelican Staff: Thanks for the info. - Nick at Pelican Parts
Comments: Just completed this project on a '02 Boxster S 6 speed which is low mileage & had never had the trans oil changed. A few observations that might help others:
* Metal transmission cover required a bit of force to remove after removing nuts.
* The Boxster 6 speed fill hole is on the driver's side Wayne's pic of the 996 6 speed shows it is on the passenger side. Mine required a lot of force to remove galled. Used penetrating oil PB, a hammer on a flat punch to the center of the plug, and a breaker bar with a 10 MM hex socket to remove it.
* Used anti-seize paste on threads of fasteners to make the job easier next time.
November 7, 2012
Followup from the Pelican Staff: Thanks for the additional Info. We appreciate it. - Nick at Pelican Parts
Comments: My 2004 986 is showing the "Check Engine Light" and a rocking, rotating light/indicator runs back and forth between high and low gears. This is an automatic transmission. An engine sensor read out says "Transmission shifter solenoid circuit malfunction". I cannot find anything on line about repairing this. Any one have a clue please?
October 4, 2012
Followup from the Pelican Staff: This is a fault code for a solenoid in the transmission. You will need a Porsche scann tool, the wiring and test tools to diganose it. You'll want to operate the solenoid with the scan tool and see if it is actuating. If not, then check the control signal to the solenoid. - Nick at Pelican Parts
Comments: on a 99 boxter will a 5 and 6 speed bolt up the same to a 986
April 19, 2012
Followup from the Pelican Staff: If I remember correctly, on M96 motors, the bolt pattern is different, but both will bolt up. - Nick at Pelican Parts
Comments: Souldn't the drain procedure read to drain the oil with the car warm as the oil will be less viscous. It states the oil will be more viscous warm.
December 11, 2011
Followup from the Pelican Staff: Yes, you can do that and it will in general drain more fluid out. You just need to be very careful working around any hot exhaust components. With engine oil, it's easy to reach all of the drain plugs. With the transmission - not as much. - Wayne at Pelican Parts
Wayne at Pelican Parts
Comments: Here's another photo of the drain (yellow) and fill (purple) plugs on the six-speed transmissions.
September 5, 2011
Followup from the Pelican Staff: - Wayne at Pelican Parts
Comments: This article is confusing on the 5 speed transaxle. Why do you state "Pump the transmission case full of fluid until it just starts to run out the filler hole", and later in the article it states that the oil should be "11 mm below the plug opening"? Please explain, Thanks!
August 23, 2011
Followup from the Pelican Staff: Sorry about that, you're right. That's for the six speed (fill until it runs out of the hole). The 5-speed should be a little bit less. I don't know why Porsche made it this way, nearly every other transmission on earth does it where you fill it up to the bottom of the filler hole. - Wayne at Pelican Parts
Comments: Just a note that the 6 speed Boxster S FILL plug is on the DRIVERS SIDE on the gearbox end of the transaxle, almost at the back of the car. You can actually access it to top off without removing anything.
It is NOT on the round differential housing cover like the 5 speed.
There is, what looks like a fill plug, on the passenger side round differential housing cover - this is not correct. Don't ask me how I know ........
August 7, 2011
Followup from the Pelican Staff: Indeed, this is in a different spot. I have a photo from the upcoming 996 book, which basically uses a similar transmission as the Boxster 'S'. I will post that photo here. - Wayne at Pelican Parts
Comments: Can I use my Mighty Vac to suck the transmission oil out of the fill hole instead of draining from the bottom. I know the oil is thick, but if I do it shortly after driving it should be more fluid right? Just checking to make sure I can reach the bottom of the sump with the Vac.
January 9, 2011
Followup from the Pelican Staff: I don't see why that wouldn't work, but you will not get all the fluid out. You'll have to get a flexible extension and insert it into the tube, like is shown in the photo above. - Wayne at Pelican Parts
Wayne at Pelican Parts
Comments: JJ, here's a photo of the drain plug on the six speed transmission.
December 12, 2010
Followup from the Pelican Staff: Thanks Wayne - Nick at Pelican Parts
Comments: Wayne I am trying to find the filler plug on my 6 speed 986. Can you tell me where that is? Thanks.
December 9, 2010
Followup from the Pelican Staff: JJ, see the photo above that Wayne shared.- Nick at Pelican Parts
I went with my 1997 Boxster 2.5 5 speed manual to a workshop to change the engine oil.
I also told them to verify the level of the oil in the transmission/differential.
They verify that the level was low below the hole and add about one quart of oil. There were no visible signs of leaks.
But you say that "This mini dipstick should register transmission fluid at about 11mm below the lowest edge of the filler hole"
So probably the mechanics didn't know that and when they saw that the level was lower than the oil, they filled until the fluid started to flowing out of the hole.
Do you think that there is any problem in the excess of oil?
September 21, 2010
Followup from the Pelican Staff: It pays to go to shops that know about the cars! :) The transmission level is too high now. I'm not sure what the problems might be, but I would take it back to them, and have them take out the quart that they added (in their error). Tell them to look in the factory manuals (they probably don't even have a set?). - Wayne at Pelican Parts
Check out some other sample projects
from the book: