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Chauch

Oil Separator - diagnosis?

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MY2000Boxster,

Thanks for the AOS info, I could not figure out where my oil consumption was occuring, pulled off my oil cap with car running-large amt of suctioning occured, and engine nearly died, just sputtered. Engine idle rerturned to normal after screwing cap back on. Definetly looks as if I found my source! I will definetly begin preperation to replace AOS.

Thanks for the great post

Jason

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Is the need to replace the AOS and bellows quite likely as the car reaches a certain age?

John:

With the bellows, it's more a matter of deterioration of the rubber caused by oil vapers and degradation of the rubber over time.

With the AOS, if you have the early style AOS it should be replaced almost as a matter of course. The early style is easily identified by looking at the circular black part at the top of the AOS. If that part is horizontal, it is the early style.

With the later style AOS, it is more a matter of paying close attention to the symptoms of a failing AOS, being more vigilant as you reach more miles.

In any case, it's a fairly straightforward DIY with the usual space constraints causing difficulties.

Take a look at Mike Focke's Boxster Pages for some good general information (even though it deals specifically with Boxsters) here:

http://mike.focke.googlepages.com/airoilseparatorreplacement

Regards, Maurice.

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Is the need to replace the AOS and bellows quite likely as the car reaches a certain age?

John:

With the bellows, it's more a matter of deterioration of the rubber caused by oil vapers and degradation of the rubber over time.

With the AOS, if you have the early style AOS it should be replaced almost as a matter of course. The early style is easily identified by looking at the circular black part at the top of the AOS. If that part is horizontal, it is the early style.

With the later style AOS, it is more a matter of paying close attention to the symptoms of a failing AOS, being more vigilant as you reach more miles.

In any case, it's a fairly straightforward DIY with the usual space constraints causing difficulties.

Take a look at Mike Focke's Boxster Pages for some good general information (even though it deals specifically with Boxsters) here:

http://mike.focke.googlepages.com/airoilseparatorreplacement

Regards, Maurice.

Very helpful! Thanks so much, great people, great site.

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having completed this DIY a couple weeks back I can assure you that on a C2 this is not a simple job (and I am told on a C4 its differant still)

The job might be done from the bottom but I did it from the top based on what I was told on Rennlist. A freind did his from the bottom but had the tranny out for a clutch, even still he claimed it was a challange.

Let me know if you want to do the job I will link you to a good bit of info on my job, and what to watch for to make it easier

Ed

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...there should be a very slight negative pressure in the cranckase on a normally asperated engine while idling. The quick test if the oil cap is opened the vehicle should not die emediately or sound as if it has extreme gasping noise, there are gauges to measure this pressure, but a trick that we used in the shop is to use a latex exam glove with a rubber band around the fill tube, it should pull in when started showing slight negative pressure, if it balloons outward the seperator is bad, or if the extreme gasping noise is heard when opening (sometimes it can be even hard to get the fill cap off when this occuring).

I think a lot of people on this board have it wrong, and this is the only post that is contrary to what most people believe.

I believe you are right and the normal behaviour is a certain amount of negative pressure and somewhat rough idle when the cap is removed.

Can you confirm this, that the rough idle is normal when removing the oil cap.

If you remove the cap and nothing happens, the car dies, or you have extreme negative pressure or positive pressure from the cap then the AOS is bad.

I'm pretty sure the easiest way to diagnose bad AOS is the presence of oil in the throttle body, y plenum, intake manifolds.

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...there should be a very slight negative pressure in the cranckase on a normally asperated engine while idling. The quick test if the oil cap is opened the vehicle should not die emediately or sound as if it has extreme gasping noise, there are gauges to measure this pressure, but a trick that we used in the shop is to use a latex exam glove with a rubber band around the fill tube, it should pull in when started showing slight negative pressure, if it balloons outward the seperator is bad, or if the extreme gasping noise is heard when opening (sometimes it can be even hard to get the fill cap off when this occuring).

I think a lot of people on this board have it wrong, and this is the only post that is contrary to what most people believe.

I believe you are right and the normal behaviour is a certain amount of negative pressure and somewhat rough idle when the cap is removed.

Can you confirm this, that the rough idle is normal when removing the oil cap.

If you remove the cap and nothing happens, the car dies, or you have extreme negative pressure or positive pressure from the cap then the AOS is bad.

I'm pretty sure the easiest way to diagnose bad AOS is the presence of oil in the throttle body, y plenum, intake manifolds.

I don't see any major contradiction between the svansyoc post of symptoms and the one you describe.

I do think that you have it exactly right.

Regards, Maurice.

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I am pretty sure mine is bad on my 99. When I remove the oil cap the engine stumbles and there is slight negative pressure. Engine does not idle well after long drives. Looking in the throttle body there is some oil on the drivers side around the hose from the AOS. Noticed a puff of blue and white smoke on the drivers side exhaust when my son started it the other day.

Loren says that its a 1 hour job at the dealer but some say it takes many hours of hard labor. The boxter write up is good but it may not be exact for a 996. Guess I need to put it up on jackstands and see what all the fuss is about. Also interesting that some remove the alternator and others go under to get to a part that is on the back of the engine.

Confused

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dr7966

After the symptoms you describe, i would wait with the AOS replacement:

Stumbling engine and a slight vacuum is normal.

A slight oil film in the intake manifold/ AOS tube is normal.

A puff of blue and white smoke from the drivers side exhaust ( = the opposite cylinder bank = bank 2 ) points out an other problem, in case of AOS problems blue smoke comes from BOTH exhausts, cause the AOS failure (oil in the intake manifold) is a CENTRAL problem.

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Thanks RFM

I thought after reading about AOS that I found the cause of my oil usage. I will keep an eye on the negative pressure to see if it gets worse. Need to have my son start it again to see if the smoke is from one or both tailpipes.

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Aside from worn rings or valve guides what would be a possible cause of oil in the cylinders of only one bank? It sounds dumb but I hope the issue is common to all cylinders.

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