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My 2002 C2 996 has started to produce clouds of white smoke on start from cold. When the car is warm, everything is completely normal. 

I don't mean a puff of smoke from the exhausts, I'm talking so much smoke that I can't see in my garage. 

I've checked the oil level, it's not high. In fact it's towards the bottom of the dipstick. I don't seem to be using any significant quantity of oil but use the car only on warm sunny days so it's difficult to know the exact oil consumption rate. 

I'm not losing any coolant and have no intermix issues. There's only not the normal - minimal - white gunge in the oil filler cap. 

I changed the AOS when this problem started, and have checked the crankcase negative pressure which is 4.5" WG and pretty much what I expected to find. 

The engine was rebuilt 10k miles ago and the the cylinders re-rounded and Hartech closed-deck rings fitted. 

Does anyone have any ideas what the problem might be?

Thanks

Paul G

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........ I should add that the car only does this when it's been left for a few days without being used. If I start it - say 10 hours - after it was last run, then there is no smoke on start up. 

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Could it be the valve seals or piston rings?  That's what i would think it could be, since you have had the AOS done!  Mine doe's the same but only one out of 30 times when i start it.  I'm not sure what it is, my local shop says not to worry.

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Regardless of whether the AOS has been changed, it still sounds like an AOS problem. There have been reports of "brand new" AOS's going bad shortly/immediately after installation. It's possible that you got a bad one... :-(

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Yes yes thought it could be a duff AOS even though it was brand new. I researched 'definitive testing' of the AOS and found that crankcase negative pressure is the only real way to find out if it's ok. My crankcase pressure is exactly what it should be when the AOS is healthy - hence my uncertainty now on what is causing this. 

  • Upvote 1

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Do the smoke come out from tailpipes on both sides? Did you remove the throttle body and the T-plenum and look INSIDE the intake manifolds to see if there's any accumulation of engine oil inside? they can hold a lot of oil.

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I literally just starting having this problem today.

Car has been not been driven a lot lately as I had left knee repair surgery in late January.  I've only recently been doing short drives into town, or a few longer moderate drives to a nearby village about 10 miles away on a straight highway.  Minding the speed limit, of course.

Today the timing was right and I drove out about 15 miles and then 15 miles back on a somewhat twisty and hilly mountain road.  This was more of a Porsche C4$ 6-speed drive.

I parked the car for about 30 min after I returned, and when I started it the above-noted clouds of white smoke came from the exhaust, more notably I think from the left side.

The smoke disappeared as I drove off, but reappeared a few hours later when started again.  I'm pretty sure this was not the exhaust cloud found with a cold start in cold weather.

I'll be checking this again in the morning.

There was no noticeable smoke when I started and drove the car only periodically from around late February.  The car had not been driven "hard" for over a month.  It has never smoked as described in the above posts.

If the car has developed an AOS issue from sitting, it has not manifested until driven as described today.  There have been no similar issues on short, modest drives into town.

Comments will be appreciated.

Edited by judgejon
6-speed transmission noted re left knee surgery

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AOS problems do happen after a car has been siting for a bit, we see it often in cars coming out of winter hibernation.  The key diagnostic is the crankcase vacuum level. we use a digital manometer to test:

 

Manometer_zpsh8cslbxd.jpg 

 

On cold start, you should see a value between 4 and 7 inches of water, but warmed up, it should be no more than 5 inches of water.  If it is over 5 inches, time for a new AOS, and do not buy an aftermarket unit, we had absolutely no luck with them.  Stay with factory.

 

You can find one of these incredibly accurate manometers on Amazon for less than $40, the rest is rubber tubing and a used oil cap.

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thanks, J.  Some modest smoke this morning, not bad.  no smoke at several starts during the day.

I'll monitor closely over weekend, and likely check-in with inde on Monday.

Cheers, jl

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Don't overly downplay the issue, failing AOS units have claimed engines by suddenly catastrophically failing, allow the engine to suddenly inhale liquid oil and hydraulically lock, reducing the engine to rubble.  

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Right.  I'll be calling very good inde shop on Monday.  I'm guessing he will have a manometer for testing, or we will like start pulling stuff off throttle body to check.

Thanks for the follow up.  I'll post what I find out.  Cheers, j

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Inspection by experienced Inde.  All seems well.  No smoke.  Crankcase vacuum seems normal.  Will surely being paying attention should any smoke reappear.

Thanks to all.

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For the sake of completeness on this subject ,here is a helpful comment I am quoting from JFP to an AOS question and the Crankcase Vent Valve -part of the system.

"The vent valve is rarely involved as when it fails, it tends to shut off or reduce vacuum flow to the crankcase.  As they are cheap, if you were to take it out to check it, I would just can in and put in a new one.  And by-the-by, it is not at all unusual to have short lived AOS units, particularly if they are non factory.  We have had exactly zero luck with aftermarket units and now only use factory. "

Part of the AOS replacement procedure should include disconnecting and inspection/oil removal from inside the intake ducts.If this is not done, the residual oil will continue to produce AOS-failure symptoms even with  good ,new AOS installed.Ahsai hinted at this above.

Edited by Schnell Gelb

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3 hours ago, Schnell Gelb said:

For the sake of completeness on this subject ,here is a helpful comment I am quoting from JFP to an AOS question and the Crankcase Vent Valve -part of the system.

"The vent valve is rarely involved as when it fails, it tends to shut off or reduce vacuum flow to the crankcase.  As they are cheap, if you were to take it out to check it, I would just can in and put in a new one.  And by-the-by, it is not at all unusual to have short lived AOS units, particularly if they are non factory.  We have had exactly zero luck with aftermarket units and now only use factory. "

thanks.  I agree, stay away from the aftermarket.  we figured out that my smoke issue was because I had not driven the car at all for several weeks, only occasional idle, car was on trickle charger.  Then I drove a few times over several weeks more and warmed up the engine to 180, but never ran hard.  then, on the day of the smoke, I'd run hard for about 30 miles on winding mountain road, then stopped at a store and did some shopping.  on restart there was the smoke.  Hasn't really happened since, and it seemed it took a good hard run to get the condensation fully out of the exhaust system.

Your advice is good.  I'm guessing your car is yellow?  Meine carreras 4$ ist Silber.  Traurig, ist mein Deutsch nicht so gut.  Je parle seulement allemand, un meilleur Français.

Good thoughts...go fast, kleine schmetterling, but safe.

  

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Excellent resolution and even better, you shared the story with us.Thank you.

There is a similar Thread where the cause of the "Hideous Smoke Bomb" (Member-  Kabra) problem on a seldom used car, was not the AOS. It was diagnosed as a version of the expensive Intermix issue

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50 minutes ago, Schnell Gelb said:

Excellent resolution and even better, you shared the story with us.Thank you.

There is a similar Thread where the cause of the "Hideous Smoke Bomb" (Member-  Kabra) problem on a seldom used car, was not the AOS. It was diagnosed as a version of the expensive Intermix issue

oh yes, my friend, aka the infamous blown head gasket situation.  "Been there, done that," in a Fiat 124 Abarth Spyder.  Hard to remember, but easy to forget. 

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It's important to see if the smoke comes from one or both pipes. My 02 C2 was a one smoke pipe and I got to know all about that situation.

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3 hours ago, 356to966 said:

It's important to see if the smoke comes from one or both pipes. My 02 C2 was a one smoke pipe and I got to know all about that situation.

would you mind noting the diagnosis of the issue and the fix?

Best....

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White smoke from one pipe during start and shortly after meant a crack in a cylinder wall in my engine. Smoke didn’t show on every start up at first and seemed to depend on where the piston stopped in relation to the crack in the cylinder wall . Coolant loss was proportional with the amount of smoke I saw. I had the cylinders opposite the smoking pipe bore scoped and got the bad news. The only way to save an engine with a cracked cylinder wall is to get it right away to a shop that can resleeve and rebuild it.

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Someone should start a "White Smoke -possible Faults List"

1. AOS failure - manometer test

2. Cracked cylinder- Bore-scope test

3. Intermix - oily coolant/watery oil

4. Overfilled engine oil -new glasses

5. Years of oil residue in Intake - clean up

6. Wild driving style - buy a Buick

7.  ...................?

 

Edited by Schnell Gelb

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