Is my AOS failing ?

[AB986]

Hello to all,

Long time reader, but first post. This forum is just amazing and I've learned a lot.

I have what seems oil on my engine's intake tubes. I don't know for how long it's been there, since last time I opened the engine bay was something like two years ago, but the car's been serviced a year ago at my local dealership and they didn't mention anything, so I assume the engine was clean then.

This seems different from the usual symptoms of a failing AOS, from what I've read here on the forum. The car runs fine, only sometimes I get a bit of smoke on cold morning for few seconds. No code on my Durametric.

This is a Boxster S, MY02, 80.000 miles.

[Glyn]

You will have some oil residue in the pipes - thats what they are there for, In old money the AOS is simply a sealed breathing system, the AOS seperates the oil mist from combustable gasses that have blown by the piston rings - this creates a positive pressure inside the engine - left with no relief this would push oil by oil seals and create leaks, All manufactures apply a negative pressure to draw away the combustable gassess as they are carsinogenic (is that spelt right?) and burn them in the combustion chamber,

Each manufactures calls their system something else - Porsche AOS.

Of course the AOS cannot be 100% in seperating oil mist from gasses so a tiny amount of oil mist is inducted and burnt, this provides an upper cylinder lubricant - which is good - but also explains why the throttle body gets a bit gummed up over a period of time - which is not so good.

When the AOS internally fails it allows much more of the oil mist to be drawn into the induction and creates massive amounts of smoke - when this happens you know the AOS has failed - clearly yours hasnt so stop worrying and drive the car.

You will hear on these forums that if the AOS is not dealt with promptly it will discharge copious amounts of oil into the intake and cause the engine to hydrallic (liquids cannot be compressed - and oil in the cylinder will will lock the engine up and cause massive engine failure as a con rod breaks) however the theory is correct but it is impossible for the AOS system to send that amount of oil into the air intake - as it is located high above the sump and it doesnt have an oil pump to raise the oil into the AOS system - The AOS can only draw air - unless you massivly overfill the sump with oil.

[Beelzy]

Your AOS sounds fine, and that little bit of smoke upon startup is somewhat normal for Flat 6 engines.

Mine does it once in a while, after my wife putts around in it. It rarely smokes after I drive it, but I drive my P-car like

a Speed Demon.

Happy Porsche-ing!

[AB986]

Many thanks for yours answers.

I understand what the AOS is for and how it's supposed to work, and that a bit of smoke upon startup is not unusual.

I'm a bit skeptical however with the fact that oil on the intake pipes is normal. When I bought the car two years ago (60.000 miles) , the engine was dusty but there wasn't any oil deposit on it. I do understand that a tiny bit of oil might get back into the air intake stream, but getting such a layer of oil on the intake tubes suggests (to me) that there is actually too much oil getting back into the throttle body, thus my suspicion that the AOS might not be doing a good job anymore. That or the air intake tubes aren't clamped tight enough somehow.

I've never seen photos of Boxster engines like this, either here or elsewhere on the Net. Do other fellow Boxster owners have oily intake tubes like I do?

To put my worries to rest, should I remove the throttle body to check if there is too much oil in it?

(BTW, I'm not a native English speaker, hopefully this isn't too obvious.)

[Rob in CO]

Many thanks for yours answers.

I understand what the AOS is for and how it's supposed to work, and that a bit of smoke upon startup is not unusual.

I'm a bit skeptical however with the fact that oil on the intake pipes is normal. When I bought the car two years ago (60.000 miles) , the engine was dusty but there wasn't any oil deposit on it. I do understand that a tiny bit of oil might get back into the air intake stream, but getting such a layer of oil on the intake tubes suggests (to me) that there is actually too much oil getting back into the throttle body, thus my suspicion that the AOS might not be doing a good job anymore. That or the air intake tubes aren't clamped tight enough somehow.

I've never seen photos of Boxster engines like this, either here or elsewhere on the Net. Do other fellow Boxster owners have oily intake tubes like I do?

To put my worries to rest, should I remove the throttle body to check if there is too much oil in it?

(BTW, I'm not a native English speaker, hopefully this isn't too obvious.)

Go ahead and remove the throttle body. It is relatively easy. Check it for lots of oil (it will have a little bit as normal), give it a good cleaning and tighten up every hose clamp you can reach when you put it back. I don' t think the little bit of oil seeping out of the tubes is worrisome, though.