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Old 03-10-2011, 12:05 PM   #1
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WTB: Failed AOS

Anyone got an failed AOS laying around in their garage?

I'd like to buy two or three failed Air Oil Separator's to tear down and determine the actual failure mode(s).

Interested in determining if there is a preventative upgrade that could be developed/created.

Please PM with price (incl shipping to zip code 91030).

Thanks.
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Old 03-10-2011, 04:14 PM   #2
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Garage
I had 1 for almost a year but threw it away after I rebuilt my engine & passed a smog test like a new car. Now I'm looking for 1 for the same reason as you. OK Foreign has had a good used 1 on E-bay for about a year for $59. I made them a offer & they countered with $50. so if you want 1 that is supposed to be OK offer them $40.
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Old 03-10-2011, 06:14 PM   #3
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I have one that operated fine on the street but was dumping large amounts of smoke on the track...not sure if you'd be interested in it. Also have the one off my 996 engine in unknown condition.
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Old 03-19-2011, 08:34 AM   #4
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Send a message via AIM to blinkwatt
If you still need one PM me or email. Just send me me whatever you think is a fair price and $10 for shipping and handling.

gl-g100rcd@sbcglobal.net

Thanks,
Robert
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Old 03-19-2011, 10:27 PM   #5
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Robert, I sent you an email.

Anyone else got a failed AOS laying around?
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Old 03-20-2011, 05:43 AM   #6
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I have one, didn't fail, but you can have it for $10 to cover shipping.

-Todd
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Old 03-20-2011, 11:17 AM   #7
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Tood - I'll take it. Sent you a PM.
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Old 03-25-2011, 09:24 PM   #8
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failed AOS

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Originally Posted by thstone
Tood - I'll take it. Sent you a PM.
I'd be interested in your results. i have had two fail on me and each time caused thousands of dollars of damage. I cut one in half to see what i could find, "not much". as a preventative measure i replace it every 50,000 miles. This AOS problem is so ridiculous that one $100.00 part can cause so much damage.
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Old 04-16-2011, 10:14 PM   #9
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^can you expand on the damages caused?
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Old 04-18-2011, 08:53 PM   #10
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when the AOS fails it creates a suction from the sump which dumps massive amounts of oil directly into your intake. Thats why the first sign you get is a smoke screen like you've never seen not to mention an immediate check engine light or what happened to me the first time the car just died on the freeway. It will most likely wipe out your Mass Air Flow sensor $360.00 part. then gunk up your throttle body which must me thoroughly cleaned after. Next it will go through and can wipe out your O2 sensors which happend to me. you have four at $200.00 each. Next it can wipe out your primary cats which happened to me as well. porsche charges $1500.00 for each one. Next it can create a strong suction in your crankcase that can cause the RMS to fail which happened to me as well, thats a $1400.00 fix. I cannot stress enough to people to change the AOS every 40-50,000 miles. why not the part is only $96.00 from the dealer takes an hour to change, two at the most. Learn from me and all the thousands that i have lost from this stupid design.
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Old 04-24-2011, 05:16 PM   #11
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AOS failure mode

I have been working on european cars for 20 years, and starting in the mid to late 90's all the euro manufacturers started using a crankcase pressure regulator similiar to the one in our m96/m97 engines' AOS. I have replaced many of them, and I broke apart many of them, at first to see what was going on inside, but I still do to verify that I have isolated the problem in most cases. there is a rubber diaphragm with a spring against it that together regulate the amount of vacuum applied to the crankcase. when sufficient vacuum is achieved the diaphragm pushes against the spring, restricting the flow of air from the crankcase to the intake. when it fails, the diaphragm usually looses it's flexibility and either cracks around the outside diameter where it has the most flex while operating, or it is just no longer flexible enough to close off the vacuum. I do not know of a way to do this that will prevent failure, other than a completely different type of crankcase ventilation. I believe that porsche has a motorsport version, but I don't think it is intended to last longer, just more effectively maintain oil in crankcase. do not consider eliminating it and running with the crankcase vented to the atmosphere. it's not that I am concerned about the environmental impact, you will loose horsepower and cause oil leaks from the engine seals. one option for a track car is to use an electric air pump to evacuate the crankcase, but I doubt the electric pump would last as long as the diaphragms do. A belt driven pump(like most cars had pumping air into the exhaust for smog regulations in the 70's and 80's) would probably last a long time, as well as increasing power and relieving pressure on seals, but it would be a complicated set up to install.
I think that if you just pay attention to your car better, you can stop changing it as a precationary measure, and just wait for it to fail. I have not seen many cars that needed additional work just because the crankcase valve or AOS as porsche calls it failed. I have replaced ones that the customer had driven till the neighbors started complaining about the smoke, and although there were O2 sensor codes at the time it came in, after replacing the AOS, and driving it to clean out the pipes, all was well. Mass airflow sensors and throttle bodies are not hard to clean, and O2 sensors usually clean themselves. AS far as catalysts go, you would have to clear it all out and see if they are really damaged. I have seen ones that set a p0420(catalyst efficiency) code when the AOS has failed, or when someone overfilled the oil, and after correcting the problem and driving it to clean it out, clearing the codes and all was fine. this is with your average customer that drives it till the neighbors are complaining about the smoke. if you are tuned into your car like a porsche driver should be, you should have no problem getting it to your mechanic before any damage is done.
BTW here is a link for the motorsports part: http://www.****************************************************.com/product/9XXSEP.html?Category_Code=986sport
at $750 though, I definitely wouldn't want to replace it until it fails.

Last edited by autodoctor911; 04-24-2011 at 05:25 PM.
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