PittsDriver

I have an '07 C4S that will occasionally blow a pretty significant cloud of blue smoke out of the exhaust on start-up. The car otherwise runs great is is not using any oil. It seems to happen most often when I've started the car cold and shut it down again before it warms up. Then on the next start, it'll then often blow smoke. It's sometimes just enough to notice and on a few occasions it was enough of a cloud to cause everyone in the driveway to run choking for cover.

One theory I've heard is that it's running very rich on a cold start and shutting it down quickly will leave some amount of unburnt fuel in the cylinders. That makes sense but the smoke is definitely blue and smells like oil smoke and the car is not at all hard to start.

As anyone seen this behavior or know what's going on here? I've had it looked at by a dealer and their response was - we didn't see it do it and there's no diagnostic codes present so come pick up your car.

mdrums

Fuel blows a black smoke and oil blows a white/blue smoke. Due to the way the flat 6 is some oil leaks past the valves. This is due to tolerances when the engine is cold and when you start it cold and shut it off and then restart it cold again in a few minutes to later. This is normal.

cvazquez

+1 This is normal, so don't worry.

PittsDriver

Thanks guys. I guess I'm wondering if it's a good habit to let it warm up completely before shutting it down again. This was the recommendation on my '97 F355 and I suspected it might be something like that. I've got over 10,000 miles on it and I've never had to add a quart of oil.

cvazquez

Yes, if you have the time it does help... better yet drive her around the block.

sclemmons

Look on the bright side. My BMW would foul the cylinders and start with a miss if you started it cold and did not let it warm up. It eventually required an engine rebuild because of leak down issues. Runs like a top now.

ADias

This thread is 3 years old... and this subject has been discussed, explained, and mitigation described many, many times.

Edgy01

You're obviously new to the 911. They do this when they have sat a long time. It's normal.