987.2: concensus on cold start/oil smoke, experiences please.

[911hillclimber]

I'm trying to fully understand the cold start/oil smoke these cars have on occasion based on my 2.9 engine in my Boxster.

I cannot find a common denominator as to why this happens and what makes it happen, it is so random.
To try to focus things can those interested pass comments in the following list?
Engine size / miles
Usage
Frequency of 'smoke on cold start'
Personal thoughts on why, ie short runs, parked on slope etc
Any facts from Porsche/specialist on the subject.

I'll start things off:

2.9, 59 plate now 53K, bought when 41K and did it then.
Approx every 10th start-up, clear from exhaust within 5 seconds or so. Not white smoke.
Car used for long runs mainly, run miles seems to have little bearing on the frequency. Car parked on level ground and does it as it will on a cold start on a slope. No oil consumption, oil level correct.
Going to try a new AOS to see if this helps.
Trade seem to know nothing when asked!

 

[Robin M]

All
my Porsche‘s have done this I think it depends on where the pistons are when the engine stops. This may keep a valve or two open. Oil gets through the open valves. Not a mechanic so this is my best guess.

 

[Briggy]

My 3.4 987.2 does it rarely, but I can trigger it more often (say 1 in 10 cold starts) under the following circumstances -

I'm one of the first to get to work, so have the pick of parking spots. I sometimes blast to the far end of the (empty) car park, turn round at speed (turn right, then left to double back) and back up the same route to the car park entrance, so I'm at the front, facing the right way. I think this blast and turn at speed increases the chances of smoke on next cold startup. I can only go on what I've observed, rather than give a technical justification though. Journey to work is about 10 miles, taking 15 minutes, so engine up to temperature.

Car on 44,000 miles, the most recent 10,000 miles driven by me. Never had to top up oil between changes.

It concerned me when I first bought the car as it can hint at a host of major issues, but as it's a known issue on flat 6 engines and the general consensus is that it doesn't cause any harm, then I don't worry.

Cheers,
Bryan

 

[911hillclimber]

Thanks for the response.
for oil to get into a cylinder it can only get in 3 ways.
seep past the piston rings
come down the inlet guides
come in via an inlet valve down the inlet tract.

the second one would show smoke all the time as the valve stem seal will have failed.

 

[phlize]

My understanding is that when the engine cools and the pistons contract (they are oval remember not perfectly round!), depending upon the position of the piston and its rings, a small amount of oil can seep from the (horizontal) cylinder below the piston into the combustion chamber(s). Hence smoke on start-up. This may be total bo**ocks but it sounds reasonable - to me anyway!
Phil.

 

[JohnCRS]

On my previous CR I found it smoked most when the engine had been switched off whe full/ very hot (I assume when the oil was at it thinnest) and if it had idled / manoevered at low speed for a few moments before flicking the switch. I got into the practice of blipping the throttle as I turned it off (only to say 2000 rpm). Early in my ownership it once produced a massive amount of smoke where it had been parked sideways on a slope after a lot of fiddling around to get it there. Very alarming. It never did it to that extent again and the overall situation improved as the miles went on. I guess I also just stopped looking out for it. No oil consumption to speak of and no other untoward issues.

 

[911hillclimber]

Good to read, hope more will chip in.

 

[BrianJ]

My 986 Boxster 2.7 facelift occasionally used to produce an unbelievable cloud of white/blue smoke on cold start (it was kept in a nice dry garage) - probably did it half a dozen times over 6 years and 80k miles. Filled our garden and adjacent road with a thick fog - very embarrassing. No obvious reason. My subsequent 987 Gen 2 3.4S Cayman never did it once in 47k miles (same driving, same garage), and neither has my current 3.4 981 Boxster S (now nearly 30k miles, not used as much as previous two).

 

[jdpef356]

Try this, but make sure you are out of gear.

Stand outside the car and start it on the key. Did you see smoke?

 

[911hillclimber]

When mine 'belches' you don't need to be outside to see the smoke....

Ran mine for the first time a week after the re-map of the DME, no smoke.
Have moved the car deliberately to a slight slope on the drive, away from it's normal parking spot that is really level.
Might change things?

 

[jdpef356]

Try this, but make sure you are out of gear.

Stand outside the car and start it on the key. Did you see smoke?

When mine 'belches' you don't need to be outside to see the smoke....

Ran mine for the first time a week after the re-map of the DME, no smoke.
Have moved the car deliberately to a slight slope on the drive, away from it's normal parking spot that is really level.
Might change things?

My suggestion of "Stand outside the car and start it on the key" Did you see smoke?"

Was not so you could see the smoke.

Quite simply, when sitting in the car many unconsciously feather the throttle pedal when they turn the key, thus causing the smoke.

 

[911hillclimber]

Ok, understand you, I always start with the foot off the throttle and leave it for a 5 or so seconds before touching it, so the time mine has smoked is essentially 2 secs after start, throttle closed.
It takes about 2 secs for the smoke to pass through the exhaust system.
Similarly, when stopping the engine I leave the car to tick over for 3 secs or longer then switch off.

The DME update open the throttle just after the engine has stopped (I think)