Smoke on start up

I have a 2007 cayman 50k miles. Great car. No issues. Except. About once every 20 startups. It blows a big cloud of smoke when engine starts. I have been told this is normal. can anyone explain mechanically why this happens ??? 90% of time it has zero smoke at startup

My guess is that the ring gaps line up and you get oil past the rings. Rings all rotate and have gaps. Line them all up and poof.

In my 987.2 Base. I've learned to let the engine idle sufficiently long on every start to come off the fast idle. This prevents the smoke on the subsequent start. In my case at least, it's not oil smoke but a rich fuel mixture causing the smoke.

Interesting thought. I think I understand your approach. However my start up smoke only occurs after the car has been sitting not driven for a while . After the initial cloud of smoke it instantly does not smoke. And if I drive it off and on that day. No smoke. But if I let it sit for several days or a week. It will rarely blow a big cloud when it first kicks over. Again. 19 times an out of 20 after sitting not driven for a few days there will be no smoke. So the other member idea may be my issue. But there has to be a mechanical explanation

I thought there was a trait of Flat sixes for a bit of oil to accumulates when left sitting for several days, and a little bit of a puff as this excess is burnt off?

My personal thinking on this is that you get the puff when the ring gaps line up. Rings rotate for even wear. If they all line up you get a puff.

I have been told it is normal. But just curious for the fact reasin why.

After rereading the discussion, just wondering what color is the smoke? White typically means the AOS , (air/oil separator), blue smoke can mean oil, while black smoke may mean rich fuel mixture. And do you detect an odor to the smoke? These are all telltales to help diagnose where your problem originates.

Thank you for input. I am pretty color blind. It’s not black. Waiting for the next cloud for my wife to determine color Nonetoday.

I had a similar experience with my 997 Turbo when it sits around for two weeks. 1 - At startup I would get a greyish blue puff of smoke. 2- I would let it run for about 5 minutes to get good engine oil flow 3 - Then I would turn the engine off, wait about 2 minutes and then restart 4 - No smoke at all 5 - Next day, started engine again and no smoke traces at all. Worn valve stem seals (Rarely possible and not always the case) - This is the most common cause of blue smoke specifically at cold startup. Oil seeps past the seals when the car sits, pools on top of the valves, then burns off when you start it. The smoke usually clears after a few seconds/minutes. In summary, these vehicles need to be driven and not allowed to sit for long period of time. Just my two cents.

ANY horizontally oriented engine will do this on occasion - and the cause is the ring gaps lining up at the bottom of the bore, and some oil in the bore creeping past them. That is, any horizontally oriented engine - unless the manufacturer does what BMW finally did on their motorcycles - is pin the oil control ring so it no longer spins on the piston, and the gap NEVER is at the bottom of the cylinder. The early BMW 3-cylinder 750 engine and 4-cylinder 1000 engines were notorious for this trait because the head was low when the bike was on its sidestand. If you shut down the engine and immediately put it on the sidestand, you'd often look as if you were fogging for mosquitoes next time you started it - oil stayed in the bore, and drained towards the rings. IF however you were a bit savy and after shutting the engine off - leaned the bike to the right (crankshaft) side for 20 seconds before putting it on the sidestand - you'd never see any smoke. Starting with the 1100cc 4-cylinder engine the oil ring was pinned and that was the end of the smoke. Valve stem seals on a horizontal engine design are unlikely to cause smoke, since they aren't oriented to allow oil to run down the valve stem. The oil won't pool on top of the valves because it never reaches them.

Deilenberger, you are absolutely right about the ring issue at the base of the piston bore at the base. My uncle's an old 750 had the issue you described. Thank you so much for providing some great information on the startup smoke and fortunately my issue is gone. Love your XKE avatar - I have owned my 1967 1.5 E-Type open coupe for 45 years and was my commuter car for many years. Finally, retired and am working on its restoration among other project cars.

My 2008 987.1 2.7L smokes in a similar fashion. I read the following somewhere but i cant remember where now and not sure if it is true, a porka mechanic really needs to weigh in on it! The smoke happens when cylinder No 6 piston stops at the bottom of its stroke (is that BDC)? and then stays there while the engine cools. Number 6 is the lowest cylinder, and the piston skirt sits in the oil pool. This allows a small amount of oil to be grabbed by the rings on start up (not sure the ring gaps lining up is a thing, if that was the issue it would smoke on every start up)??? It only takes a small amount of oil to cause a big puff that quickly disappears. So, the engine has a 1 in 6 chance of piston 6 stopping close to BDC indicating it could case the randomness of the problem. I recall the person suggested that if the engine was slightly underfilled with oil at the service, it can stop it occurring. I recently had my car serviced and it now puffs smoke (randomly) but probably once every 10 starts (sometimes it will do it twice in a row). Before the service, it puffed smoke (randomly) one every 20 starts. The length of time it sits is not a factor. My car sat 2 weeks over Xmas - no smoke, Yesterday it sat 1 Hr smoked twice in a row. My friends give me **** for it because it is guaranteed to happen every time I leave their house. I know "they all do it" but it still pisses me a bit!

Great comment. Thank you.

My 08 does the same thing. Once in a random start I'll get a big white cloud of smoke that quickly dissipates. It will go weeks without happening and then one time it will do it. I figured it was the AOS, and even bought all the replacement parts. 🤷

So did the aos replacement parts change anything ?

It seems like a replacement of the AOS is something that nearly all owners will face at some point, and it is recommended to replace it according to mileage or age of the vehicle. And many who have gotten in there report an oily buildup or residue in the valve and piping, so swapping it out can only help matters going forward. It’s not overly expensive or difficult to replace, so go for it. Let us know the results.