kab1994

Hey everyone,

I've tried searching and haven't found anything quite like what I'm looking for so I thought I would start a new thread.

I did an oil change about two weeks ago. When I started the car cold for the first time after the oil change there was a large cloud of smoke that came from the back. It must have only lasted for 5-10 seconds because when I noticed and got out to look there was no more smoke coming out. I drove the car for a few hours and it never smoked up again, after stoping and starting several times.

The car sits for about a week maybe more, and I started it again tonight, same thing. This time I jumped out immediately and there was no trace of where the smoke was coming from, leading me to believe it is just a large cloud on immediate startup.

The car runs fine while driving it after like I said above. No more smoke, no misfire, no cel. The car is not eating coolant, nor are there any signs of intermix. The AOS was replaced exactly one year ago. The smoke does not have a distinct smell.

Any thoughts suggestions? I'm not naive to believe it couldn't be the AOS again, but I don't know if this is a symptom of that. I pulled the oil filler cap off at idle and could tell there was some vacuum pressure. Yes I used Mobil 1 0W-40.

This has never happened before, only after this last oil change.

Any help is appreciated. Thanks!

Ahsai

What's the oil level and do you drive the car very aggressively?

kab1994

It could be that the oil is a little full. I probably put around 9 quarts in. I will check the dipstick in the morning. I do drive aggressively for the couple of hours a week I drive the car.

Ahsai

Definitly check the oil level. Driving it aggressively can also contribute to the issue. Also a good idea to check the crankcase vacuum in case the AOS is bad.

Bradstock

I've had the same problem for about a year now on my 2002 C4 cab, 45,000 miles. 3 to 5 seconds of whitish smoke on cold start, still no definitive diagnosis. Smoke comes from the left exhaust, AOS replaced less than one year ago (no change in symptoms), removed Fabspeed cold air intake back to stock intake (still no change), right bank plugs oily, crankcase vacuum normal (according to manometer test), engine uses roughly 1 quart of oil every 2000 miles, no other symptoms or CEL, car sounds and runs beautifully. Mechanic number one couldn't figure it out, mechanic number 2 said oil is pooling in the intake which is probably leaking into the right cylinder bank causing the smoke, possibly partially resulting from the fact that nearly all of my trips are short causing overabundance of water and gas in the oil. I'll be bringing it to Cape Auto in Orange county next, hoping to get some answers. Good luck.

jhbrennan

Occasionally I'll have the same thing happen but usually after the car is stated and then shut down a short time later (15 seconds or so). Typically when I position the car for washing or to work on it. AOS was replaced a couple of months ago and otherwise car runs fine - no oil consumption at all. I've been told that the smoking on start is related to the design of the boxer engine. Suburu forums discuss the same issue.

Southern Man

I had the same issue. Solved it by keeping oil at mid-point on the dipstick. I was so **** for awhile that I always kept my oil level at the top mark on the stick. Half a quart less seems to do the trick, at least it did for me.

tokika

Same here. I find that if I let it warm up until the RPM drops before ahutting it off to wash, it doesn't do it on the restart.

Dans996tt

AOS could be bad but this is normal if you start the car and only run it for a short time without warming it up.

Mike Murphy

This was a common discussion point in the air-cooled forums. Oil is getting past the rings or the valves. Why? Could be high oil level, or could be wear, could be the type of oil used. Since this didn't happen before your oil change, that's the most suspect. Either high level, or the type of oil used.

For those that have this problem regardless, it's not too worrisome as long as your oil consumption is not too high. There's not much to be done about it anyway. If you think about it, these pistons sit pretty low in the vehicle and are prone to having oil sitting at the bottom of the piston/cylinder and rings. Oil sits there for many hours, and eventually will find its way past the rings or ring gaps. Some oil is more opportunistic than others. These engines sometimes wear unevenly and have out of round cylinders that can lead to more oil getting past the rings. If you think about leakdown numbers - sometimes ranging from 1-2% and as high as 5-10%, you gotta figure if air can get past the rings and valves, oil, with enough time, can get past. It doesn't take more than a couple drops of oil to produce white smoke at startup.

At the end of the day, as I said, id this happens to folks that have tried everything, it's not as uncommon as you might think and ended up not worrying me when it happened on my 88 Carrera.

kab1994

Hi All,

So I went to hear this morning. Oil level is certainly high, the line is just below the max fill dot but not over it. Coolant looks fine, again not loosing any.

So I started the car, it had been sitting about 12 hours since I drove it last night. No smoke whatsoever. Very weird.

Nickshu

Lol...mine does it too. Since I previously owned an air cooled 911 I just figured it was a carry-over characteristic to the water cooled cars.


Just checked my dipstick, it's over full so there ya go.

Macster

Normal.

If it was a bad (even though new) AOS the smoking wouldn't end almost as soon as it started the smoking would continue.

Surprised you didn't check the oil level after you changed the oil. I suspect you would have found the oil level a bit high.

My experience with my Boxster and 996 Turbo is fresh oil -- with the engine *not* overfilled with oil but with the engine oil level at the max line with the oil up to temperature -- is the engine very very rarely smokes upon start up.

But as the oil approaches the 5K mile mark the smoking is more likely to occur. I change the oil every 5K miles.

Short trips or spirited usage with no "cool down" time can result in smoking the next time you start the engine.

While an engine can smoke from worn rings, bad cylinders, worn valve stems, guides, bad valve guide seals, an engine suffering from any of these conditions will smoke at other times too. Unless you see smoke from the exhaust when taking off from a stop or smoke when you up shift under hard acceleration or coasting some distance with the engine supplying the braking then stomping on the gas pedal and seeing a could of smoke, your engine is not sufferng from any of the above problems.

The smoking is not from bad rings, worn valve stems or guides or seals, it is from the AOS. The AOS is just not that efficient under all conditions in removing the considerable amount of oil vapor from the crankcase fumes as they flow through the AOS on the way to the intake.

As a result the crankcase fumes as they leave the hose from the AOS at the intake impact the wall opposite the hose connection and the vapor being unable to make the sharp turn collects on the wall and becomes liguid again. This is quite common. Porsche techs tell me that invariably when they have access to an engine's intake they find the intake walls oily, sometimes wet with oil.

When the engine is shut off the heat soaks the intake -- which normally stays pretty cool -- and warms it and this of course warms the oil. The now warm oil then flows down onto one or more closed intake valves of just possibly one cylinder. If the intake valves are open the oil flows into the cylinder.

Upon cold engine start because everything is cold the oil doesn't burn completely and the converter can't do anything about it and the cloud of oil smoke is the result.

Techs see this even with brand new cars that get shuffled about on the lot. What they tell me is if the smoking is short lived, stops almost as soon as it starts, if the CEL remains dark and the engine doesn't manifest any running issues -- rough idle, varying idle speed, etc. -- the smoking is just due to a bit of oil from the intake that drained down into the cylinders and is really of no concern.

Couple of things you can do to reduce the frequency of this smoking upon cold start. Do not over fill the engine with oil. If you fill the engine with oil while the engine (and oil) is cold leave the level 2 bars low. Then after you have run the engine and it is fully up to temperature and you check the oil level -- after the engine has sat off for say 5 minutes -- you should find the oil level right at the max line. If still low you can add oil to bring the hot oil level up to the max line.

I am not a fan of running the oil level purposely low even a few bars below max with the intent of preventing smoking upon cold start. The oil level as long as it is not over filled is not the reason for the smoking. Running the oil level at the max level helps ensure the engine the best chance of having an adequate supply of oil sans any air at all times under all operating conditions.

Do not run the oil too long. As the oil accumulates miles it also accumulates water and other combustion by-products. The water contributes to the oil's tendency to foam and this generates more oil vapor which just adds to the oil vapor the AOS is already unable to deal with.

Like I said above I seldom see oil smoke with fresh oil in the engine. But as the oil gets close to having 5K miles once or twice before an oil change the engine will smoke upon cold start and this even though my usage remains quite constant.

If you can avoid short trips.

If you enjoy the car in a spirited fashion try to arrange some more sedate usage on your way back to the garage to give the engine time to shed the heat load and the oil that is almost certainly in the intake time to make its way into the engine where because the engine is hot will be burned with no signs of any oil smoke.

Do not dismiss this as not being a factor.

With my Turbo as per the owners manual I let the engine idle 2 minutes before shutting the engine off. This is to let the turbos cool down and they do this best at idle when exhaust gas temperature is its lowest. The turbos continue to receive oil too which helps remove a bit of heat but mainly the heat is given up by the exhaust turbine to the realtively cool exhaust gases flowing past it.

The Turbo has an oil pressure gage and as the engine idles I can watch the oil pressure gage and invariably as the 2 minutes elapses the oil presure is down just a skosh. Not much but it is a real drop. Say at the start of the 2 minute idle time the oil pressure is 2 bar. At the end of the 2 minutes the oil pressure is just under 2 bar. This suggests the oil has gotten hotter.

The oil level changes too. (With the Turbo I can only check the oil level with the engine running at idle speed.) The oil level sometimes drops a bar. It doesn't really "lose" a full bar's worth of volume the level was probably just at the border line. But the level drop is real because the oil in the tank loses some air and the volume drops in the oil tank. This is an indication of how frothy the oil can get inside the engine. And frothy oil generates lots of oil vapor.

Ahsai

The dot on the dipstick is the overfill level. The oil level should not be higher than the upper notch (theres a lower notch as well).

Ahsai

See post #13 here.
https://rennlist.com/forums/996-forum/827546-dipstick-length.html#post11556505