996.2 Cloud of Smoke on Cold Start

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!

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

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.

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.

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.

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.

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.

Quotes source post: 14080345

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.

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.

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.

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.

Quotes source post: 14080484

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.

Quotes source post: 14079946

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.

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).

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

Scored or ovaled bores could be a contributory factor, and in my opinion this is likely to be the next thing we all need to repair, (next gen IMSB problem if you like) with this Engine. Mine has just been pulled apart due to developing a tick combined with a filter full of metal, prior to that, slight smoke on start up, nothing too bad, was fine otherwise, nothing noticeable most of the time. Failure turned out to be thrust bearing that has let go, but during the tear down, we found all 6 bores to be oval and two are scored. Hopefully yours is just over full/ Porsche AOS issues as Macster points out. Nice to see another Green car BTW and good luck.

if I track my car or drive like a jack ***, it will smoke on the next day's cold start up. The OE AOS just isn't up to par to deal with really aggressive driving. I am saving up for the motorsports one as I do track the car 3 or 4 times a year. I only put 8L of oil in my car. That is about 2 or 3 bars down from the top. Anything more than that and she smokes very easily on cold start up after some aggressive driving/turning

Mine will smoke occasionally after sitting, however, I read that letting it idle for a minute or two after driving spirited or not will cut down on that issue. It seems to work for me. AWD: Not to hi-jack this thread, but you still have your toy and am enjoying it?

Very useful Macster and Ahsai. Imagine all the worry you have allayed The different dipstick markings is very interesting.Thanks. https://rennlist.com/forums/996-foru...l#post11556505

and if you google "my porsche 911 smokes on cold start up" - you will get results of brand new 991's smoking on cold start up. Cars with less than 20k miles on them - smoke on start up.

Hello all, I have a 2001 996 C4 with 84000 miles that's my daily driver. Saturday changed the alternator (that has a story!) and MAF by indy shop- right after drove back for an hour got the light on, code was P0507 - Cleaned the TB, code. Sunday noticed white cloud of smoke on cold start and rough idle! same this morning but the engine didn't struggle! Milage has dropped from 23 to 17 !! Bad AOS?? Does it have to do anything with MAF that was changed?? Give it a time?? Thanks a bunch

Our cars are very picky about the MAF sensor. What brand/type of MAF sensor was put in? Why was it replaced in the first place? Unplug it and see if there is any difference in the way the engine runs. Since the alternator was replaced, did they break the oil filler tube? Inspect for any cracks. Make sure the oil filler cap is on tight. Check the air intake for leaks and all the clamps are tight. After checking all this, reset the DME by disconnecting the negative battery lead for a few minutes. That will put the DME at default base values. Then go for a drive so the DME can re-map based on the new MAF. Don't forget to plug the MAF back in.

Thanks for the reply. Porsche MAF, after they changed alternator, they called me that engine check light is on P1128 + P1130 ( never had that issue before). Could it be due to air leak that you said and not the MAF?? Checked/cleaned oil cap yesterday. I will check the rest tonight. indy shop is a reputable with 30+ yrs and is in racing himself. Now I got smoke coming out on cold start!! GreaTT!!! Taking it back to the shop. not related to this post but during alternator ordeal temperature would go up to just after 0 on 180. I thought water pump is going bad (with squeaky noise), but shop checked everything and said cooling fan high speed is out. Changed the auxiliary fan but still temperature is same!

All of your PCodes are pointing to a intake system leak or bad MAF. https://rennlist.com/forums/996-foru...e-opinion.html Cooling fan high speed - they are talking about either the left side or right side radiator fan. Check the fan relays, after that it is usually the fan resistors if the fan runs at low speed. Run car and turn on AC. That will make the radiator fans come on at low speed. Check that there is air blowing out just ahead of each side front tire. When was the last time you cleaned your radiators?

And also, it is very easy to leave a vacuum line disconnected when replacing the alternator, or screw up the routing. https://rennlist.com/forums/996-foru...omponents.html

[Image-only post; no author-written text. Original image references:] https://cimg7.ibsrv.net/gimg/rennlist.com-vbulletin/1209x903/relay_support_1_plug_position_0c1c4d8305c0ee038a9714e8e0515cc448ff00b0.jpg https://cimg8.ibsrv.net/gimg/rennlist.com-vbulletin/1298x885/relay_support_1_relay_diagram_7c5bdbcf3be971bcf51384fa8b052cd0e5979d5c.jpg

Thank you, you�re very helpful. Have not cleaned it other than vacuuming from outside! I will look into it - Thanks again 👍

DBJoe996: Could this cloud of smoke be related to the recent change of alternator and MAF?? It started right after I pick up my car, did not have any issue before- I checked the oil level and oil cap as suggested by other members.

Quotes source post: 14914184

I�ll give an answer based on having two failed aos�s over the past few years. Seems unlikely, however a trip back to your mechanic would be a smart next step. Have them check the crankcase vacuum level. This will quickly determine if your aos has failed (which will cause white smoke on startup). Could be just a coincidence that this happened after your recent service. Either way way your mechanic should be able to quickly diagnose the cause.

This morning on cold start, more from passenger side , smells like 2 strokes motor bike ! Normal in 10 seconds- drove 30 miles, engine light came up, code:P1128 ! Taking it in tomorrow- 😤

Quotes source post: 14915394

That's more than a puff! Good luck!

I was told AOS needs to be replaced. Thid is the pic from passenger side! Appreciate your input. Thanks guys Oil leak - passenger side !

That AOS crossover hose that ends up at the right rear of the engine (viewed from behind) could be split or just seeping and you would eventually end up with this mess I think. Your symptoms sure sounded to me like someone broke or disconnected a vacuum line in the process of other work, but now I'm not so sure.

The AOS and bellows is on the drivers side, and so the oil would leak down on the drivers side of the engine. Maybe yours is a leaking oil pressure sender that is located up on the passenger side. Or as said, the AOS breather hose that connects by the AC compressor. The breather hose might be split somewhere.

^^ Or the spark plug tube right above that leak. Nice Agency Power headers! I just put a set on my car - less "droney" than the stock manifolds

P.S. this is the sound that started the ordeal- I had no smoke issue or engine light prior to changing alternator which I was told is the culprit!!!

Quotes source post: 14920541

Could be alternator, or could be any one of the belt pulleys or water pump. The belt needs to come off and each pulley turned by hand to check for grinding, squealing, loose or moving around. This I think has nothing to do with your previously stated problems.

spark plug tube seals

How did that work out?

Ocfservice: I will check after work. Thanks everyone for your help. 🍺

Oil in TB Everything looked dry. I can see part of a hose behind alternator that seems to be oily (pic pointing with stick) and found oil in TB (picture) that didn�t have on Sunday when cleaned it out. Under the car passenger side same mess as previous photo 😤😤 More smoke on cold start and stays longer!

UPDATE: Same squeaky noise came back last Thursday. called the Indy Porsche who changed the alternator as culprit for the noise, he insisted, that sound was fixed by changing alternator and this must be a new noise!!! He did not want to hear the sound that I recorded . It�s EXACTLY the same noise from same area. Anyhow, had to stop in Hwy due to smoke and engine was coughing on me causing de-acceleration - I thought I lost the engine! Took it to a neighborhood garage off of a gas station! They are very well respected and knowledgeable, he had worked on my M6 before! But never crossed my mind to ask him about 911! He explained the whole working mechanism of AOS and hoses and sound etc....! Parts arrived yesterday and they are working on it as we speak ! Will update when it�s up and running. as for the Indy shop, I guess we�ll have to have a judge to decide! Thanks for all your help everyone.

UPDATE: AOS and hoses replaced- engine light (MAF) gone- smooth engine, no squeaky noise, no smoke on start up 👌 problem solved-

Quotes source post: 14920032

Right on the money - 👍 squeaky noise was also due to AOS failure not alternator!