White smoke on startup

jw2015 · Aug 10, 2005

I've asked this question before and I've been told that it's pretty normal to have a puff of white-ish smoke occasionally on startup - a feature of the boxer cylinder configuration? Can anyone elaborate as to why it happens. I was getting it on the odd occasion and it wasn't really noticable but very recently I've had a couple of clouds of smoke on startup that were pretty big and embarrassing, even if they do stop pretty quickly. All I can think is that perhaps these were occasions where the previous trip in the car was very short. We have a real shortage of resident street parking here and occasionally to avoid tickets I might have to move my car a few hundred metres in the morning, which might be the only drive it gets for a couple of days. So is it a completely random occurance or might it be due to trips that barely get the engine temp up. I also have to park on a slope on occasion, might this have anything to do with it. What is it burning anyway, to me the smoke doesn't seem dark enough for oil.

Guest · Aug 10, 2005

John, I've haerd or read somewhere that the oil scrapers on the pistons can rotate such that the gap in the ring can end up at the bottom allowing residual oil to seep into the combustion chamber. (perculiar to the boxer config.) hence the small puff of smoke on startup.

My 996 does it, but not all the time - only periodically. White smoke yes, parking on a slope? I'm unsure if this will have any effect.

oliver · Aug 10, 2005

Every 'horizontally opposed' Porsche I've ever had has done it - from 356 to 996.

It's more noticeable the longer the car has been left standing.

Rodney Naghar · Aug 10, 2005

JCB posted this a while ago....

'Tony

It is a characteristic of any horizontally opposed engine layout (the so called
boxer configuration). Air-cooled VW's do exactly the same.

The popular explanation is that if a piston is on the induction stroke when it
comes to rest the pressure in it's cylinder will equalise by sucking air past
the piston rings. This can bring a small amount if oil with it which is what
gets burnt off when you start up.

However I haven't found a Subaru owner who will admit it.

JCB..'

russtbird · Aug 10, 2005

John - you might be interested in this page which I found whilst searching for an answer to the same question: http://www.986faq.com/10-0/problems.asp
By the way, mine doesn't seem do it now the warmer weather has returned (but it could be coincidence) and I thought it was to do with the time I had left between drives, but it's proved me wrong on that one too!

jw2015 · Aug 11, 2005

I can't see a pattern either, from all the posts above, it's bound to be a completely random occurance, depending on resting cylinder position. I reckon it doesn't really depend on how long it sits either, I had two big clouds of smoke yesterday within a couple of hours of each other, previous trips being very short, thanks to resident parking problems and drying off the disks after washing the car. These were significant burn-offs though, passers by thought I'd blown the engine up, very embarassing. [&o]

mojo · Aug 11, 2005

I posted exactly the same on www.porsche-1.net earlier this week.

http://www.porsche-1.net/forums/index.php?showtopic=4266

JCB.. · Aug 11, 2005

I can't see a pattern either, from all the posts above, it's bound to be a completely random occurance, depending on resting cylinder position. I reckon it doesn't really depend on how long it sits either, I had two big clouds of smoke yesterday within a couple of hours of each other, previous trips being very short, thanks to resident parking problems and drying off the disks after washing the car. These were significant burn-offs though, passers by thought I'd blown the engine up, very embarassing.

I can almost guarantee getting a cloud if the car hasn't reached it's operating temperature on the previous run. I don't know what it is about such short runs that causes it.

It is embarassing when it happens but it isn't anything to worry about.

When it happens at 90 MPH is the time to check the credit limit on your plastic!

JCB..

Guest · Aug 11, 2005

I would imagine the short run means the oil hasn't heated up (even if the water is an operating temp) and so is still more viscous than on a long run, and hence its "gloopiness" means it gets retained where it can get burnt off more readily?

jw2015 · Aug 11, 2005

Now that you mention it I've had more occurances in warmer weather, would oil viscosity be affected all that much by a 10degree difference in air temparture?