Smoking 2001 996 Convertibe, AOS?

[jsoderbe]

Hi,

I recently bought a 996 Carrera with supposed "engine failure". However, searching here it looks like it might only be the AOS that need replacing. The sympoms are:

- Heavy smoke from both exhausts, maybe a little heavier from the left exhaust

- PO says it started smoking suddenly on the freeway, and was towed to a service station (obviously not familiar with p-cars....)

- Oil missing in engine

- Coolant not mixed with oil, level looked ok

- NO abnormal engine noise

- Starts right up and idles smooth

So, any opinions? Should I order an AOS replacement (where) or do some additional testing?

Thanks,

Johan

[Loren]

Take the air cleaner off and look in the throttle body. Is it very oily - if so, then likely the AOS is bad.

Oil missing in engine is still a concern. Top up the oil being careful to not overfill.

[jsoderbe]

Thanks Loren,

I will do that, car is being shipped so it will take a few weeks. Great advice!

Regards,

Johan

[jsoderbe]

Hi again,

Now the car is over here in Europe, after three months in shipping! I left the car at a friends shop yesterday, and I am waiting to hear about the end result.

However, he did not find the amounts of oil in the intake that I expexted. He did find coolant and oil in there, but the oil was more dry than fluid. The AOS was all gooey from leaks on the outside, but he could not say anything about the internals.

Unfortunately the oil filler tube broke, so we cant start it up yet to confirm AOS failure....

Can it really be anything else? I am just concerned after speaking to a guy that cracked a cylinder in his 2001 996.

Johan

[logray]

Oil cooler can also cause oil to mix with coolant.

Not sure, but perhaps AOS can also cause intermix in some form, since both oil vapor and coolant run through it?

Cracked head can cause oil to mix with coolant.

<post edited for accuracy>

Edited October 9, 2011 by logray

[jsoderbe]

Hi Logray,

Sorry about the confusion, this s not my 2000 996 with intermix. This is a 2001 996 parts car I bought with supposed engine failure. It is kind of funny, the car with engine failure could maybe only suffer from a bad AOS, and the ok car turned out to have intermix.

So AOS could cause intermix? Could that be the problem with my 2000 996?

Regards,

Johan

[logray]

Oh, sorry for the confusion. The AOS does have coolant running through it to prevent it from freezing. It also has oil vapor and a direct passage to oil channels, so if there is a crack in the plastic, perhaps yes it could cause some oil to mix with coolant or the other way around. But I'm not 100% positive about this. You should get more opinions about it.

<edited for accuracy>

Edited October 9, 2011 by logray

[Kim]

I recently had an AOS failure on my 2000 996 Cab. You listed the following symptoms as reported by PO:

- Heavy smoke from both exhausts, ( I had no smoke)

- Oil missing in engine ( car used no oil )

- NO abnormal engine noise ( car had loud squealing noise coming from AOS )

Also, my car showed oil pressure dropping to almost zero whenever I made a hard deceleration / stop. It would then recover.

Your symptoms do not sound like a bad AOS to me.

[logray]

- NO abnormal engine noise ( car had loud squealing noise coming from AOS )

Possible air in coolant system or coolant system underfill. Possible bad AOS.

[jsoderbe]

Hmm, my 2000 996 sometimes have a high-pitch squealing noice. Not all the time, though. It sound like it is time to change the AOS on that one too.

Back to the '01; I think I will have the answer within a day or two. I am still fairly confident it is the AOS, since I can't figure out another way for oil and coolant to get up into the intake plenum, and to have oil smoke in BOTH exhaust pipes. The symptoms are spot on the ones listed in te excellent 24 page DIY posted here, cant remember the name of the poster. I seems like the AOS can break in severl different ways.

I still havent read someone that got oil in coolant from a broken AOS though. That would have been interesting, with my 2000 996 with intemix....

Thanks,

Johan

[RFM]

Oil in the coolant from a broken AOS is not possible cause lack of pressure on the oil, there is only a thick oil mist present inside the AOS where by a swirl motion and some obstacles, air and residual oil becoming separated, the air goes in to the intake manifold, the residual oil drips in a natural way in to the sump. Coolant in the oil could be theoretical possible for 996 AOS since they are heated on top by the coolant, but i've never seen that phenomenon.

[logray]

Thanks RFM for the great info as always! :)

[jsoderbe]

Hi,

I got the car back from the shop today, and it looks like the AOS was the problem! I'm saying "looks" since I prefer to drive it some more before I can say for sure.

My friend owning the shop said that it still smoked heavily when they started it up. Worse than that was that there was a very hard sounding noise coming from the engine when revving it. He is a very experienced engine guy, and he was not sure what it was. It sounded like crank bearings, but it can't be since it vanished after he re-started it.

I just drove the car back, and took it for a 15 mile drive. It ran excellent, I'm impressed by the power even though it has 110 k miles on it. Afterwards it came some minor smoke from the exhaust, but I guess it can be oil residue from the intake that get's into the engine when the car is driven hard. When it is left to idle it clears up in a minute or two.

I'm kind of concerned about the noise, and since I couldn't hear it myself I can't explain it. Anyone that have an idea? Something clutch related? Cam chains, valves? Anything that might suffer when engine hasn't been started, or when oil pressure isn't high enough?

The car has not been started since early June, and was clearly suffering from that. The clutch slipped slightly at first, but gripped after the first initial run. No leaks of oil or coolant.

Thanks,

Johan