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Unexplained smoking?

JamesO

JamesO

New member
A bit of a weird one, my car has started producing large amounts of fine almost steam like smoke from the exhaust. It only does it when idling after a long run. The smoke/steam continues wisping out after shutdown for a while.

Coolant and oil levels don't seem to be dropping, compression test comes out exactly the same as a year ago, both hot and cold, with or without oil.

Spark plugs look the perfect colour to me with no fouling.

AFR at idle is 14:1.

When the car was last on the dyno it produced no visible smoke at all.

I'm a bit stumped, turbo seals maybe?

 
Used to have the same problem until I replaced the headgasket and headstuds.

Since the headgasket looked fine when I took the head off I came to the conclusion that I had not torqued correctly the aftermarket headstuds I initially used and the fire rings were not sealing properly when the engine was idling. Perhaps it was also smoking on the move too but then it was not visible at all.

If I remember correctly you run 968 or 2.7 pistons, so in your case it's possible that you might just have begun to blow the headgasket in good old style because of too much boost considering the compression ratio?
 
968 pistons, I suppose its possible although I'm running less boost than I used to.
I might open it up and take a look as I have a noisey tappet thats been bugging me for a while.
 
Do you know how much compression ratio you have with the 968 pistons and the 2.7 head?
 
Well just been out and given it death. Not a whiff of smoke or steam. Its a mystery, maybe worth my while re-torqing the head bolts.
 
fine almost steam like smoke from the exhaust. It only does it when idling after a long run. The smoke/steam continues wisping out after shutdown for a while.
Click to expand...

I was thinking CHG too, - but in view of the after shutdown steam, what about - coolant water from the turbo housing getting into the colds side and showing as steam at tick over, and continuing this after shutdown where the steam passes thru the valves which happen to be open and exit the hot side / exhaust?? Once the water jacket pressure is released the steam stops. On tick-over only? thats because at higher engine speeds the extra heat and airflow eliminate the small amount of steam....?

And, as you have now given her a good clear out, the water seal has reseated its-self....for a while

Just trying to think - how can it happen - wierd for sure

I would not pull the head yet

George
944t
 
It is very odd, when it happened it was the middle of a hot afternoon. just been out for a longer run at the same sort of temperature and again nothing. The steam was bad enough for a neighbour to comment.
 
Are you sure it's steam?

Oil being vaporised by getting into the hotside comes out white....
 
Steam/oil again combined with a low load misfire and knock on the datalog. It seems to happen only after the oil temperature creeps up in traffic, coolant temperature is pretty stable.
Maybe the oil is making it past the seals only when very hot briefly fouling the plugs.

 
That's what I thought with the miss and I would prefer it to be, I hate trying to get at the turbo.
The only odd thing is the lack of coolant loss, unless its being replaced with bubbles.
Any other car I've had drank/blew out the coolant pdq if it was bad enough to create a misfire.

Time for a sniff test kit then.

A good excuse to fit a steam vent, sort the noisy tappet and paint the cam tower I guess.

Cheers.
 
Well thought I would wrap this up.

Smoke turned out to be oil mist from the crankcase breather, verified with a temporary catch can. Turns out last time I checked the oil I hadn't quite pushed the dipstick home and overfilled it, only by a small amount but enough to cause the smoke.

Its absolutely fine now at the max mark.

The miss fire it turns out was the cooling fan causing interferance on the crank pully mounted VR sensor, possibly a bad ground to the fan. The data log showed 150 rpm with the engine off and fan running, pull the fan fuse and its fine.
It's not caused a problem before as its not been hot enough until recently to cause the fan to come on when driving and I try to avoid traffic.

 
Well spotted James.

I drove mine last weekend on the Autobahn (we had a 3L turbo meet over in Germany) and though I felt uncomfortable taking it out in such a hot weather (we had more than 35°C in the shade) I was relieved to notice coolant and oil temps remained at reasonable levels, even at moderate but sustained loads.
 
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