Hey all,

I am having an issue with oil getting by the diaphragm in my air oil separator. A little back story, my AOS went out a few months ago. Symptoms included: squealing by the rear tire, smoking like a james bond movie, oil pooling in intake, i.e. complete failure of the original AOS. I replaced the AOS with an URO parts AOS. Once I replaced the AOS, it was no longer dumping oil into the intake. However, I noticed that on higher RPM downshifts (3,500-4,000 RPM) oil would then go into the intake and smoke. The smoking would not be constant, but it would just burn off the oil that went by the AOS. I figured that the diaphragm was bad, so I called FCP Euro just to see what they thought. They also thought that my diaphragm was bad, so I ordered a Porsche Genuine AOS.
Fast forward to today, I installed the Porsche Genuine AOS and it is still allowing some oil to get by the diaphragm on higher RPM downshifts... What could possibly be causing this?

Random facts that may help diagnose: I always rev match when downshifting, engine does not seem to be showing other symptoms, does not smoke on start-up, does not smoke during idle and/or normal city driving, no leaks. Only exhibits oil "seepage" on higher RPM downshifts.

Vehicle: 2006 911 3.6L, GT3 intake plenum, fabspeed intake, tune.

Thanks in advance!

 

I have a 997.2, C2S 3.8L so my experience may be somewhat different. Anyway, I replaced my AOS at about 20k mi.
The engine was letting out a cloud of smoke at start up. About a year later the smoke was returning. I decided to bring
the oil level down one section on the electronic gauge. I have not had any smoke since. Seems to me Porsche has an
accuracy problem with the gauge system. I never had oil in the intake however. If lowering the oil level slightly isn't the
solution, you better get to a dealer or a very highly regarded indy shop.

A few years ago Sharkwerks recommended not modifying the intake. Apparently you gain nothing but a lighter wallet.
These engines are finely tuned systems.

 

I think your next step is to get a manometer on the system and see what kind of vacuum numbers you're seeing, which will tell you if the AOS is working correctly.

Oil smoke in high vacuum situations can also be from worn valve guide seals

 

2009 C2S 194K miles

My oil level gauge is wonky and always has been. For ten years, I have been threatening to replace the sensor in the oil pan, but I just live with it by making many readings. The measuring system on the .2 is different than the .1 BTW. I never had smoke though.

Peace
Bruce in Philly (now Atlanta)

 

Ok, I will probably have to do that. Do you have a specific manometer that you like to use or is generic sufficient?
Also, I have seen a lot of people talk about the oil cap test. They say that if the oil cap is impossible to pull off, then the AOS is bad? But what is "impossible to pull off"? I have pulled mine off and it has enough vacuum to make it more difficult than pulling it off when the engine is off; but, it is nowhere near "impossible." When the oil cap is off, the engine has a rough idle. That is perfectly normal as I understand it, right?

 

I never quite understood the benefit of a digital oil level gauge over the dipstick... Porsche should have had both.

And yes, I am aware of the performance of the different intakes. PO had a terribly crafted air intake, so it was cheaper for me to buy a used fabspeed over a new/used OEM air box.

 

@Porschetech3 maybe you can add something to this conversation. FYI, he is the inventor of the UAOS for 996 and 997.1 models.

 

Unless you took apart the entire intake system and cleaned it out before installing the new AOS, you are going to get some residual oil trapped in the system every time you go to a high intake vacuum situation, like down shifts........................

 

Woa, JFP.... a blast from my Boxster past... welcome! Your expertise is needed here. Our cars are getting older now...

Peace
Bruce in Philly (now Atlanta)

 

5 inches of water plus or minus one on a 997.1 implies a good AOS. I haven't seen readings for the 997.2 cars but I've got a spare oil cap waiting for me to pick up at the local dealer so I will have a reading from mine soon (2010 C4S PDK with 155K miles and original AOS).

These cars can smoke at start up, especially if parked on a slight side to side slope. It's just what it is and pointless to read anything into it. Just a part of the flat 6 design.

With the 9A1 motor we got more scavenging pumps. These push oil into a spacial reservoir. The idea was to prevent oil starvation in high G conditions. But that means oil measurement can only be done once those pumps have a chance to do their job. That means warm motor on a level surface at idle long enough to have the system stabilized. A dip stick can't measure this.

It's a different story on the M9X motors. But I'm guessing Porsche had their reasons.

Under heavy load at high power output the AOS can be stressed. Are you seeing excessive oil usage? If no, then the AOS is probably doing its job. If yes, then there are too many variables to make a conclusion.

 

Yes, I can shed some light on this subject, I happen to proficient in this field..

As mentioned the first thing to do is test the AOS with a manometer ( should read 4-6 inh2o) , also as mentioned if you had an AOS failure there could be oil pooled in the intake on shelf that will spill over when driven aggressive in turns or braking.( G-force) and can take a while to clear up..

That said, while you have the manometer, you should do a "blow-by test" as outlined in this thread https://rennlist.com/forums/996-foru...=engine+health To make sure the engine ring seal is in spec and the blow-by isn't over 80 Liters per Minute....

The UAOS Ststem designed for M96/M97 engine is 4x more efficient at keeping oil from the intake, and returning it to the sump where it belongs...

The Factory AOS is barely good enough to control the blow-by of a really healthy engine, and even Porsche has lowered the oil level on 996.2 up cars due to the inefficiency of the Factory AOS...( by 1/2 qt)..

The UAOS Track Version can handle 1 qt overfull oil level on a healthy engine easily...

I just recently had a Customer do the blow-by test on an 06 Cayman that was 160 LIters per minute blow-by ... in a case like this a rebuild is in order ( he had the beginning of bore scoring)

Happy to answer any other questions..

 

This is what this forum is about! Perfect info. Thank you!!

I will do both manometer tests this weekend and post the results. Theoretically the blowby test you mentioned is better than a compression test since it will test for blowby on the valve seals, right?

 

Yeah, I cleaned the intake thoroughly and even replaced the upper AOS tube.

 

Yes, the blow-by test is the real test for ring seal in real world dynamic conditions of combustion, full loads, and high RPM ,where-as the compression test is only at starter speeds of 300-400 RPM, or a leak down test which is purely static...

 

Do you sell this solution?
3.8S, freshly rebuilt, new AOS, but I might be interested in changing it out due to what you just said.