Smoke upon startup

I know our cars tend to smoke a little upon startup at times but I have to ask this question anyway. I was out running errands the other day and during one stop I started the car and it smoked for about 5 seconds. Now this doesn't alarm me because it's been doing that a few times here and there since I got it. But it was still a little embarrassing because it was in front of an outdoor dining area and people were probably thinking, "Look at this guy with the $hitty Porsche." Anyway I told my wife the story about how I was cringing but this was a necessarily evil that I had to live with because of the flat engine design. She then tells me, "My old Subaru had the same type of engine and it never did that." I had no answer for her and thought I'd pose the question out to the Rennlist community. Why do our cars smoke at times yet the Subaru flat engines don't seem to have the same issues with oil leaks and smoky startups?

what do you tell a woman with a black eye?

My 1998 Boxster used to do this a lot and it was quite embarrassing. I don't want to start an oil war but on the recommendation of a multi-Porsche owning friend I switched from Mobil 0w-40 to Royal Purple 10w-40 and 90% of this stopped. It occasionally would do it if I started it long enough to move it out of the garage to wash it, let it sit a while then start it up again. I do not know a lot about oil and the additives but the RP must have reconditioned some of the seals as after about 3,000 miles the car seemed to run smoother and quieter. The old girl has 130,000 on the OD and runs strong. I am only speaking from what I experienced with my Boxster. My 996 has Mobil 0w-40 but with it being 100 degrees in NC yesterday and only being June, I am thinking about trying something a little heavier.

Mine doesn't smoke with 125k on startup but occasionally if I downshift from 6th to 3rd at highway speeds, I get a puff here and there. If you're embarrassed by it, park it around the corner or put on a 993 badge and all will be normal.

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Mine has only smoked on startup a couple of times, and every time was basically this exact scenario.

Mine (80k miles) just did this for the first time - at least that I have noticed. The car had been up on one jackstand for two weeks at an awkward angle and the oil had been topped off and was completely full prior to being put up on a stand. When I took the car down and started it, it blew one cloud of smoke for a second and stopped. I run Mobil 0w-40. Do you guys noticed a difference in smoke levels depending if it is sitting on a hill or not?

120k on my 99 & I have never seen any smoke. knock on wood (grain)

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Haha! No comment, nothing good can come out of my response here! That makes sense as thin oil can more easily slip through the rings and seals. Are you concerned about the impact the 10w-40 has on the variocam? I've always read that the thin oil is needed to operate the variocam effectively. I've been checking my oil pressure these last few days (I saw 106 on my outside temp gauge driving home yesterday!) and it seems okay but I hear what you're saying about something a little heavier. Where in NC are you? Charlotte here! The smoke doesn't happen all the time. Usually it's after hard driving like the track or stop and go driving where I rev up high and then shut the engine off. But even then it's not consistent. I had some of my track buddies tell me to keep the oil level showing only halfway on the indicator bars to minimize this from happening. And for those wondering it used to do it before replacing the AOS and still does it after the new one was installed. I remember a few years ago a guy with a brand new 997 GT3 turned his on after we all went out to lunch and he created a smokescreen. So it's not only our M96 engines that do this. As for the 993 badge, if I do it will it positively affect my resale value?

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Nothing, you already told her once....

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I am in the North Raleigh/Wake Forest area. I haven't had any issues with the 10w-40 and a friend who has been a Porsche Tech for 30 years told me he has customers who have used either 5w-50 or 15w-50 for years with no adverse effects. He said it is mostly climate dependent and he even has a few customers who switch back and forth between 0w-40 in the winter to 5w-50 in the summer. What I find interesting is the first Boxsters came with 5w-30. As for keeping the oil level low on the indicator, I don't think I would go that route. I have always kept my oil to the top of the dash indicator and was surprised how accurate it was to the dip stick. I have been reading more on the DT 5w-40 and it seems Jake at Flat Six has done a lot of research on oil so I may use it on the 996 next oil change. I still need to install the spin-on adapter and magnetic drain plug.

Smoke at start up many times indicates a failing, or about to fail, AOS. Just throwing that in there for consideration. 133,000+ on mine and never any smoke at start up. However I have had to replace the AOS due to a coolant leak on the AOS.

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An occasional brief episode of smoke upon engine start is due to a sub par -- but not necessarily failing -- AOS. The AOS fails to remove all the oil vapor in crankcase fumes as they pass through on their way to the intake and combustion chambers. The tube from the AOS to the intake feeds the fumes into the intake air flow. The oil vapor being heavier can't make the sharp turn and impact the intake wall and collect to form oil. As the engine runs this stuff gets pulled into the engine and burned and because the engine is warm and the exhaust and converters are warm there is no smoke. But shut off the engine and wait a while and the oil will drain down and collect on top of the intake valves if they are closed or run on down into the cylinder where upon engine start the oil may cause smoke depending upon how cold the engine has gotten since it was shut off. While the smoking is or can be a bit embarrassing as long as it is short-lived, infrequent, and the engine doesn't manifest any other untoward behavior it is nothing to really worry over. What you can do to minimize the possibility of smoking... Do not over fill the engine with oil. Allow the engine to idle a bit before shutting it off. How long? 15 to 60 seconds maybe longer if you were hammering hard on the engine. Run an approved oil and do not run the oil too long. Over time the oil becomes contaminated with unburned fuel and water and this tends to cause the engine to create more oil vapor which overloads and already inadequate AOS. Do not run 10w-40 oil. If you live in a hot climate consider running Mobil 1 5w-50 oil (not a typo for 15w-50 oil!). Obviously the oil is a bit move viscous at the low temp end and at the high temp end of the oil's multi-grade viscosity which could help to reduce the formation of oil vapor. However, if you do switch to 5w-50 be aware that Porsche wants you to use 0w-40 if you live/drive in temps below -25C. If you live or drive in such a place you should switch to a "winter" oil and that would be 0w-40.

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Is that supposed to be funny? Anyhow, my 996 engine used to do that at the track occasionally. It would sometimes smoke quite a lot after sitting between laps. It always burned off and didn't affect performance. However - 6 months later the engine died. Not sayin it was related.

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DUH?

https://rennlist.com/forums/996-foru...ssues-etc.html

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I'm not concerned about the smoke as like I mentioned it has done it since I've had the car. The AOS has already been replaced and is maybe 2 1/2 years old at this point. Again this is not something that happens often but I'm familiar enough with it that I know not to be alarmed. If it is a sign that my engine is on its deathbed then it has been giving me that sign for the last 70k miles. My original intent with the post was to ask why other flat engines don't seem to have the same issues. Is it tolerances? Different engine materials? Thanks for the response. This line above I found pretty funny. How often do you see a Porsche regularly driven in -25C temperatures?!? Wow! I know it can be done but that is a pretty cold day.

Had a similar smoke episode about 6 or 8 months ago. Never had one before or after. It was between runs on an autocross, and smoked out the competition good!

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Porsche sells cars all over. Obviously not all places are as mild as NC. There are a number of places where it gets that cold and one can still drive his car, even his Porsche. -25C is -13F. Heck last Dec. I got close to driving in that temperature. I was in the mid-west (mid-Missouri) for nearly a month last Dec./Jan and for a few days the temperature never got above 1 or 2 degs. F. It was cold, as cold as I have been in quite a few years. The engine (996 Turbo) had 5w-50 oil in it -- in recognition of the mild temps where I live and drive -- and I was a bit concerned, but my concern was unwarranted. The engine was fine. Tolerances and such don't come into play in this smoking upon start up business. I dare say the engine tolerances/clearances between the various engines in modern cars is pretty close to the same. That is one is not going to find say engine A has 0.0015" clearance between the piston and cylinder while engine B has 0.005" clearance (ignoring a worn engine). (Actually years ago I rebuilt a pick up truck engine (318CI V8) and the piston/cylinder wall clearances were near the top of the allowed values -- I couldn't afford to bore the block and fit new pistons -- and the engine didn't smoke at all. The engine ran so smooth more than once I tried to start the engine while it was running. In spite of the higher than I would have wished clearances oil consumption was not an issue either.) Tolerances are the same as well. Every automaker uses the same or nearly the same engine production equipment and strives to produce engines that run well and will last. This requires adhering very closely to a narrow range of tolerances. (New and used engines (cars) get emissions tested too and car makers want to be sure their used models don't end up doing badly in these tests.) Unless the smoking occurs at other times, and reports of this happening are rare, the culprit in the case of the Porsche is the AOS. Generally these suck. Just to reinforce this and I while I arrived at these "rules" or guidelines on my own the Porsche techs confirmed them when I asked them about smoking upon startup. They told me they see it all the time with not only used cars, cars of customers in for service, but from new cars as well, and provided the smoking is upon startup only, is short lived, and is not accompanied by any untoward engine behavior or a CEL the smoking is really nothing to worry about. I will add that my observation over the years is my cars are more likely to smoke as the engine oil accumulates miles. My usage of my cars is pretty consistent day to day and is of the type of usage that is *not* conducive to engine smoke upon startup so when I see smoking upon startup it is almost always closer to the time when the oil is due to be changed. And I change or have changed the oil every 5K miles.