996 Air Oil Separator Question

I've read about the air oil separators failing on these 996's in a few threads. However, none of these threads are really detailed on this topic. Where is this air oil separator exactly located at? What does it look like? (A pic would be great!) How hard is it to change? Is this an expensive part? Any recommendations on the best place to purchase one from? I want to replace it before it starts causing me trouble!

It located on the drivers side (1-3) on top the engine towards the flywheel. Very difficult to change without dropping the transmission. Sunset or Suncoast Porsche sells them for about $120.

Thank you rb101!

My vehicle is a 2003 996 Cab I had coolant leaking (dripping) on the left side of the motor when the oil-air separator failed, 51,000 miles. I replaced the coolant expansion tank and several coolant hoses during this repair while the engine was lowered. Part cost $114.56 Total labor for all the repairs 5.5 hours (oil/air separator, coolant expansion tank, hoses and diagnostic). My suggestion, if the engine and tranny are out replace the parts and hoses, if not leave it alone. It is never just replacing a single part. Good luck.

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Thanks! My engine has approximately 50K miles on it now. The engine is going to be out, so I would like to address any potential upcoming issues at this time. Where did you find the air oil separator for $114.56? That's a good price.

The part cost was with 10% PCA discount from local independent mechanic. While the engine is out you want to complete the 60k service as outlined in the owners manual. My suggestions not considering a budget and in no order: 1. Replace the belt and tension pulleys 2. Replace coolant hoses. The hoses are not cheap but with the motor out this is the time to do it. 3. Replace the coolant expansion tank and upgrade the cap 4. Replace the water pump....on most vehicles they go bad at 80-100k miles. 5. Replace the clutch assy if it has not already replaced. Base on discussion with my mechanic they have been going bad at 35k to 50k miles. Mine went kaput at 40k miles. 5. Upgrade the clutch fork 6. Replace the engine mounts. 7. Detail the motor 8. Replace the engine sensors that are hard to reach with the motor installed. 9. Address any leaks or potential leaks My intension is not to spend your hard earned lunch money. What I have learned in my Porsche ownership is to take advantage of the over lapping processes when you can. Good luck

bxtech, here is an article I have wrote for the PCA. Maybe it can shed some light on your quest. Porsche Engine Oil/Air Separators 101 The Engine oil air separator directly affects the engine crankcase atmosphere because basically all Porsches from 1980 on including the current 986-987-996-997-Caymen & Cayenne engines all are positive crankcase type systems meaning the engine crankcase has vacuum supplied from the intake manifold to collect and burn the residual combustion by-products or blow-by in the crankcase by running it through the engine again, basically to lower the overall vehicle emissions. On most occasions, when the oil separator fails, intake vacuum in the engine crankcase rises to an unusually high or abnormally high figure and more likely than not ends up drawing engine oil into the intake system usually fouling spark plugs and even possibly causing damage to the oxygen sensors (O2), catalytic convertors and even possibly various other sensitive fuel injection components. Interestingly enough, the only way to test the oil separator is to periodically test the engine crankcase vacuum with a water filled Monometer AKA an ultrasensitive vacuum gauge. On BMW’s and Porsche’s, the engine crankcase vacuum is normally around 4-7” (Inches) of water. When these oil separators fail the crankcase vacuum can rise to 9-12” and even higher depending on the extent of the failure. When the oil separator is starting to fail on Boxsters (986-987), generally you will start to see a substantial amount of smoke from the exhaust tailpipe. When the oil separator finally fails, the engine exhaust smoke can reach dangerous proportions that almost look like it was manufactured from an anti-mosquito smoke machine. Unusually enough, on the 999-997’s, when the oil separator fails, it hardly ever creates any exhaust tailpipe smoke, almost being like a silent killer or costly surprise. On another note, it has been known on rare occasions, that when an oil separator fails that it is possible to have a slightly rich running condition that might turn on the check engine light or CEL. The only way to know what is happening is to check the fuel trim numbers on the OBD-II “Freeze Frame” data and crankcase vacuum to see exactly what’s going on, otherwise your just guessing. Tony Callas

Thanks Mookster for the extensive list. Very helpful. A lot of those things on your list are things that I was already planning to address since the engine is out. I don't want to have to pull the engine again in the near future! No fun!

Thanks Tony Callas for your very informative article. It gives me a clear "picture" of what is actually happening, and what this particular part actually does. Being a "silent killer" is kind of scary. What is the general recommendation for these? Replace it when the engine is out just to be safe? It doesn't seem like these go for many miles. Mookster's failed at 51K miles and mine is at about 50K miles right now! I am planning to change mine so I don't have to worry about it for awhile. What do you think? I would perform the test, but I do not have the proper equipment to do so, and it would probably cost me more in labor to have it done than just to replace the part!

Tony Callas, I am going through some sort of problem similar to what you described and i am leaning towards an AOS,but i dont have the experience nor the equipment to do it. My car was running fine a couple of weeks ago when i just went and parked it in the garage, yesterday i started it and first it was iddling really poorly and it would die eventually after 15 20 seconds so i re started the car several times and gave it gas while idling and it still had a very rough idle then if i depress the gas pedal too much it would back fire, finally it started smoking real bad, white color smoke that rapidly made everything foggy, i didnt go and check if smoke was coming out of both tailpipes but it seemed to idle slightly better,but then again if i would let it idle without giving it more gas it would die. I had a continues CEL and then it turned into an intermittent one. Could you please give me some advice in regards this problem? i am taking the car in to have it scanned and serviced monday morning although i am having it towed tomorrow afternoon. Thank you for your time and help.

afast16v I don't know how cold the temp has been lately in Oregon but my first experience with fuel injected engines was finding out how they start hard in cold weather. If your spark plugs and wires aren't good and the fueling with air don't clear chambers you can be looking at the same problem. It isn't always the air oil seperator. You can wipe a finger on the inside of the tail pipes to check for a fuel smell or signs of oil after a hard start like that. Being it was a cold start and it didn't kick over right away I'm thinking it wasn't the AOS. Probably a full tune up will fix things. If everything else was running good I'd think the engine would fisrt start then after a good strong start you'ld get trouble from an AOS related maledy. At least i don't think an air oil seperator problem is an instant engine killer after sitting for a couple of weeks. Change the air filter, spark plugs and even the wires if they have been on the car for it's life and see what else the shop has to say.

The only way to see if the AOS is OK is to check the crankcase vacuum. We have come up with a Manometer assembly that taps into the crankcase via the engine oil cap. This is the only way I know of to properly check the engine oil separator, without guess work. It takes me minutes to perform this procedure. I travel all over the USA and Canada teaching technicians my ideas on this, all promoted and sponsored through a company called Worldpac Training Institute. My next class is in Gaithersburg, MD next month. WORLDPAC - Advanced Technical Training Program Tony Callas

Very good info. I have a 2002 996 C4S and I just realized that my oil filler cap has some white grease on the inside of the cap. Does this mean that my engine is due for a rebuild? My car has 36k on the clock.

No. The white greasy substance on your engine oil cap is most likely water and oil mixed and is probably just from short distance driving. When your car is at operating temperature for a while, it is allowed to burn most of the moisture out of the engine oil. Is there anything strange looking other than just plain green or pink coolant in your coolant expansion tank (don't open unless the engine is dead cold)? Does the engine dip stick oil look normal? It should!

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Not according to this gentleman who changed he's with the engine in the car. YAHOO...finally did it.... - Rennlist Discussion Forums

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The white smoke and backfire issue would concern me a LOT. You might be dealing with an intermix issue or a damaged head. Don't run the engine until you get it checked out. If it is intermix, you could damage the main bearing to the point of a complete motor rebuild.

I replaced mine on my own without dropping the engine/trans. The total time from start to finish was approximately 5 hours taking my time and not rushing it. The part cost me about $135 at my local Pcar dealer. You can confirm that the AOS is faulty by removing the oil cap. The car could stall or you will be able place your hand over the opening and feel the suction. My comments and instructions are included on the following thread: My AOS adventure... - Rennlist Discussion Forums

I left my 2001 Carrera in the garage for 2 weeks without starting it. When I started it sounded like the oil was missing. It billows out white smoke from the left pipe and sounds a little like it is missing. This car has only 28,000 miles. I am worried...

Back to the AOS.It is often cited as a problem. This part has a diaphragm that fails and causes the problem$ discussed.10 cent part but $$$$ of damage potentially. Has anyone developed a work-around to use a more durable part at a reasonable price? There has been discussion of using a BMW part/generic pcv valves/Catch cans but no specific how-to. The so called Motorsports AOS is just too expensive

I would advise replacing the idler pulley bolts at least with a higher grade bolt. I had one fail (snap off) almost at idle, but was able to limp home with no consequences. I didn't know what the noise was at the time, or I'd probably have called the tow truck.

Idler pulley bolt failure - interesting suggestion. Do you have the specs on the replacement you used? for example M12 1.5 40mm grade 10.9 ? Plus use some blue Loctite?

You can change the aos by simply removing the left intake......i can change them in under 3 hours.....

A failed AOS can lights up oil warning lights due to idle rough? Sent from my iPhone using Tapatalk

The oil pressure light may illuminate because the idle is usually very low when an AOS fails.

Homemade Manometer / tester https://porsche996aosmanometer.shutterfly.com/ Porsche Engine Oil/Air Separators 101 , this is my first newbie post so don’t hang me on the nearest tree . FYI info only. 1 House of Hacks > Youtube > How to make a vacuum (or pressure) gauge https://www.youtube.com/watch?v=2jVl-0PdrRk 2 Hardware Store 1 2.25 x 1.75 Tappered Rubber Plug $ 4.50 1 5/16 brass coupler $ 2.50 20 Ft 5/16 Clear Tube $ 8.00 Tape , 24 “ Cardboard Box , Red Dye , 12” Ruler , bricks to hold the box upright the only way to test the oil separator is to periodically test the engine crankcase vacuum with a water filled Monometer AKA an ultrasensitive vacuum gauge. On BMW’s and Porsche’s, the engine crankcase vacuum is normally around 4-7” (Inches) of water. When these oil separators fail the crankcase vacuum can rise to 9-12” and even higher depending on the extent of the failure. https://porsche996aosmanometer.shutterfly.com/ Every ½” of rise = 1lb of vacuum > is what I have read online xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxx Drill 5/16 hole in large end of Rubber plug all the way through Drill 3/8 hole in small end of Rubber plug 1/2 in up Clean hole with a rat tail file, blow clean Insert 5/16 coupler in top – wide end Take box loop tube as shown & tape solid Stand up. Add bricks for balance weight Fill tube - maybe 1-2 oz dyed water just a little at a time suck on the open end if need to pull the water down – Very lightly Balance the water, add your ruler to the ZERO line Assemble the tube. Take to car , remove oil cap, start , test results Document findings w date / pictures for later comparisons on vacuum , save w your records [/img]

Or you could own this one:

Hi TCallas looks like a nice machine, where do I buy one ? i could not find it on ssfautopart.com can you send me the site url & part # please ? thanks mark

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LN Engineering sell them for around $400, or you could go online at Amazon and buy everything to make one of your own, with equal accuracy, for less than $100:

Thank you for the info. Do you believe my home-made meter is fairly accurate ? I appreciate your time to reply.

Within reason; your home made unit can only be as accurate as the ruler and optical distortion allows. A digital meter can be accurate +/- 0.01 inches across 0-55 inches of water.

Keeping this thread alive, I am seeing the Porsche Motorsport AOS on some sites. Anyone know how big a PITA this would be to install as opposed to the stock AOS?

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On many cars, "the view simply is not worth the climb" when it comes to the Motorsports AOS. It is very expensive, and some year cars it simply will not fit without a lot of modifications to make room for it. We use the current OEM unit on both street and heavily tracked cars without problems.

Craig, If you even considered the expense and difficulty(impossibility?) of the Motorsports AOS, I guess you are up for a challenge ,have a budget and are technically gifted. Here is a thread that may be what you need? It eliminates most of the AOS problem and simplifies the whole system. And you do it once. And it is smaller. And... New AOS failing? - 986 Forum - for Porsche Boxster Owners and Others

2001 C2 Triptronic I am attempting to replace my AOS. I could use some guidance that I dont seem to locate online. The rear plenum is - stuck ? the clamps are loose ,and rotates, and slips left/right, however it does not want to move forward/-disengage. I might get it out, my concern is never get it re-installed.. Any advise ? Second, it appears a palm size ..Vacuum item is attached to the back. I cant see it . Any advise or pictures I can reference. ? thank you, mark

Mark, This is really a job for those who are familiar with it. The risk is dislodging/breaking fragile plastic parts. To your question - loosen completely but do not remove all 4 clamps. loosen both flexible rubber hose connectors. Push these as far apart as you can. But the parts shown are not the AOS. You may find the big hose connectors are stuck on - as if with adhesive.They aren't. They require a thin,smooth bent spatula gently inserted between the hose and the tube to gently break the seal.Patience, finesse and persistence.

Hi Scnell Thank you for the feedback , exactly what I determined. (beak a line - ouch) So I am stopping my DYI and will take it to the shop in Jan thank you for your feedback. Mark

Ask here for a good recommendation to a local Indie ? Think of it as acquired wisdom, not defeat !

dont jump too quickly on the smoke from tail pipe,I would start my 2002 s out to wash and start it to go back in,I did this a couple of times and then there was smoke!,replaced the aos and it still did this.come to find out that the short starts didn t give it enough time to clear the buildup,after that if i ran it on a regular basis there was no smoke!

AOS diagnosis is easy. A crude measure is to remove the oil filler cap and place the palm of your hand over it to feel for excessive vacuum. An Indie would do that test free.If in doubt he would measure with a manometer. Just Search for diagnosis details.They are much easier & cheaper than a needless AOS replacement - particularly since some OEM replacements have been reported as defective !