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smoke on startup

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I own a 2001 Tiptronic Boxster with around 150 miles. To my knowledge it is the original engine (is there any way to verify this?).

Sometimes when I start it (2-3 times a month), I notice a puff of white smoke, which seems to be common for a flat 6.

Tonight however, there was a LOT more white smoke than usual, and what alarmed me is that it didn't stop after a few seconds.

I tried idling, revving, turning it off/on for a few times, reversing, and driving for a few meters out and back into my garage but the white smoke persisted and only stopped after ~10-15 minutes and.

Car performance, temperature reading and engine noise were normal as far as a can tell.

Now when I start it there is no smoke and everything seems normal.

I am afraid to drive it worrying that I might do more damage.

I am really worried that it might be an engine issue - especially since it's a high-mileage car - as I cannot afford to pay $7k at the moment.

What do you guys think?


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Search AOS failure.

from :

http://mike.focke.googlepages.com/problemareasMike Focke's Web Site:

3. AOS "The air/oil separator is essentially what was called a crankcase breather hose in earlier days. It's simply a vent from the crankcase to the intake. In the past, the crankcase was simply vented to the atmosphere releasing any volatile pollutants directly into the air. Nowadays, the crankcase volatiles are vented to the intake where they are burned in the cylinders. It's a hydrocarbon emissions reducing measure. To reduce the sheer amount of oil that gets drawn into the intake, they developed the air/oil separator which is designed to condense the higher boiling components and the oil mist (very fine droplets of oil that form when warm oil is mechanically whipped up continuously like it is inside the engine) and allow it to drain back into the crankcase.

There are two "failures" with the air/oil separators that I can distinguish. The first is simply a torn accordion looking tube (sometimes referred to as the "bellows tube") that goes from the crankcase to the bottom of the separator. This causes an oil leak and also a vacuum leak to the intake. The vacuum leak to the intake causes a lean running condition, which the ECU detects and adjusts to by enriching the mixture. Ultimately, the ECU maxes out its enriching ability and triggers a check engine light with the fault codes associated with enrichment limit: P1124, P1126, P1128, and/or P1130. (Note that this end result is general for any intake vacuum leak, not just the that caused by a torn AOS tube.)

The other failure mode is the failure of the air/oil separating ability of the separator. I don't know the exact nature of what happens in this case since I've never disassembled an air/oil separator. When this happens large amounts of oil can get sucked into the intake causing major oil smoke from the tailpipe. If this is allowed to go on long enough, spark plugs will become fouled, and I believe the catalytic converters could be permanently damaged. In the worst case scenario a cylinder could even fill up with enough oil to cause a condition known as "hydraulic lock" in which the piston now tries to compress an incompressible fluid in the cylinder on the compression stroke. The oil can't be compressed so something has to give, and kablooie... big problems."

the above contributed by Brett from San Diego

Symptoms of AOS failure are typically huge oil clouds on startup or under hard acceleration, braking or cornering. Replacing the AOS can be a ~$120 Do It Yourself that takes several hours. It is more dirty work than smart work and anyone can do it. Instructions are on this site. There is a racing AOS from the GT3 that can be fitted that is said to be more robust but it is much more costly and is not a direct fit.

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txhokie4life, thanks a lot for your prompt reply.

Do you think that I can drive my car to my mechanic? (there is no more smoke) or will I be better off getting it transported by a truck?

thanks again,

I appreciate the input everyone...

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txhokie4life, thanks a lot for your prompt reply.

Do you think that I can drive my car to my mechanic? (there is no more smoke) or will I be better off getting it transported by a truck?

thanks again,

I appreciate the input everyone...

As long as it is not too far -- you should be ok. I have not had an AOS fail yet -- so I can't say definitively.

You might smoke like a chimney -- but < the 15 minutes you already were idling should be no worse.

What is happening is that oil is being placed back in your intake,

as the AOS fails it will get worse and worse. You just don't want to be burning

oil too long as it will foul the plugs and mess with the cats.

someone else might be able to define too long.


Edited by txhokie4life
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Far too many people hung up on this smoke thing - and the paranoia continues with a description of the type of smoke - Blue or white.

People describe the colour hoping to minimise negative replies

I think this needs to be cleared up once and for all.

You either have steam or smoke, Smoke is oil burning and may have a tinge of blue if oil burning is excessive, and steam is the condensed water in the exhaust that has been evaporated by the high temperature developed in the Cats soon after starting and this is like any steam - a whitey grey colour - so you cant have white smoke and you cant have blue steam.

Now the issue - If the engine sounds fine and runs fine then dont worry about it - They all smoke intermittently and sometimes it is alarming - most of the time its embarrasing to have such a prestigious car that puffs out so much smoke that people have to move away.

Its a characteristic of the flat 6 engine.

Its possibly not the AOS as this only comes into play and does the job its intended to do when the engine is at normal opperating temperature - you havnt mentioned smoke whilst running so i assume once warmed there are no oil burning issues.

If the AOS has died then you will have smoke after warm up and when you switch off oil will make its way into the throttle body via the AOS pipework - this will be the oil mist condensing in the pipes and then drip into the throttle.

Park the car on level ground, a side to side incline allows more oil to drip onto the cylinder bores and as a result some oil gets past the piston rings and oil scavenge ring - especially with a high miler car

Really - dont worry about it, far too many people will offer up suggestions that start from the most serious of issues like a blown engine, some have little automotive knowledge - they just like the sound of a term they once heard and offer up the suggestion for everything from a noise in the rear to the radio not working.

The car is just a car - usually they are pretty bullet proof, You have a high mileage car - so i would guess that all serious issues will have been sorted by now - of course there will be a bit more maintenance now so some parts will need to be changed - Just take a deep breath and relax - the car is not going to explode

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Glyn, thanks a lot for clearing things out.

I have just started the car and tried opening the oil cap with the engine running. I could do it with very little effort. Does this rule AOS out and I can drive the car with no worries?

Thanks again everyone

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Krypt, go ahead and drive the car, the issues yoyu describe are the normal panic issues of a new owner.

So many stories about mechanical failures that are so expensive to repair.

Lets put things into perspective - the AOS is cheap - just getting the job done in an OPC is expensive - over here £50 the part - £450 the labour, easy enough job to do yourself and there are loads of us on the forum that will help and assist.

I dont think you have any issues - the puff of smoke even if the AOS has gone will do nothing more than produce a bit of smoke. and if it keeps doing it then change the AOS at your leisure

You will hear tales of excessive oil being drawn into the engine with a failed AOS and so much that the engine Hydralyics - this is another one of those myths.

Park on level ground - the side to side incline will increase the frequency of smoke on startup as the horizontal engine has three cylinders pointing towards the left rear wheel and three to the right wheel and oil dripping back to the sump drips onto the cylinder bore right behind the piston - then when everything cools and all the expanded (through heat) metals shrink it leave a little bit bigger gap for the oil to seep into the combustion chamber so on startup it looks like a smokescreen - just a tiny bit of oil produces loads of smoke .

As i said before - If it sounds right and drives right then what you describe is nothing to worry about.

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Whilst I agree that a puff of smoke is quite common on startup, and nothing to worry about, if you are getting plumes of white smoke that doesn't clear, then it could well be the AOS. Sometimes they make a screeching noise like the reed of a woodwind instrument, caused by air passing through a split in the internal plastic pipe.

It is a simple job to remove the inlet hose to the throttle body, and look inside for oil residue. It costs nothing to do, and will let you confirm or eliminate whether this is the problem or not.

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  • 2 weeks later...

i too have a 2005 carrera 997S (3.8L)launch car 6 speed cpo'ed with lots of white smoke on startup only after atrack session...i also burn 1.5 - 2 qts of oil per day (125-150 track miles) more than i have seen with any other 997 at the track.....much more....car recently was tested..i had to request leak down compression (normal) , scoped sylinders (ok) oil separator changed, no oil leakage , rms ok, and they drove the car 400 miles on the street for me and no oil usage. any ideas..i heard changing to motorsport AOS will helpcure the problem...is there anything else that could be checked.....no smoking on the street at home..about 1 qt/1000 miles on street. my car has a few dealer installed mods including fabspeed headers, exhaust (stock cats) GIAC flash, evo intake, running r comps at track with ceramic brakes, gt3 control arms and i run with the instructor groups......i am concerned whether i should keep the car or get rid of it before cpo is over risking engine failure later....thanks... MK USA

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