964enthus

This topic has been discussed at length ,but never really had a technical conclusion
to sum up what we agreed upon before:
-white smoke at start up after car been garaged for a few weeks is due to oil seeping back from tank or pipes down to the crankcase ,filling slowly that crankcase up to a level above the base of the pistons
-overfilling can be the culprit ,but ,to a degree ,most 964 do that
Now the question: where does this oil mainly come from ,from which pipe,due to what siphoning effect .
What is the mechanism of this seepage ?
To me ,this is not a purely academic question : a lot of oil burning in the cat will damage the cell.i have read ,that the cat is built precisely to absorb pollutants including BUT it has not been built to absorb oil or petrol WHEN COLD .My understanding is that on a cold egine ,oil will clog the cells and this clogging will not be cleansed when the cat reaches normal operating temperatures
I would like to find a way to stop this seepage happening
I'll start first with a suggestion :i have read on a diagram that there is a small pipe running from the top of the oil tank to the throttle housing :,called "air bypass line with 1.5mm restrictor in oil tank ".I suppose this line is to evacuate excessive pressure in the tank back to the intake port ?As it is higher than the tank and should generally be empty , at first sight ,this should not be the reason of the seepage ,but it could be that ,because of the open vent ,oil in the line between filter and engine are allowed to flow down to the crankcase
Could this line be the culprit ?
As ever ,thanks for your thoughts !
Peter

Rocket Rob

Its my understanding that when the engine is shut off, the oil in the oil tank will slowly drain back into the bottom of the crank case. This then has the tendency to then seep paste the piston rings and into the combustion chambers. The old aircraft radial engines had a similar problem where the lower cylinders would get oil in the combustion chambers. What can be done to avoid it? Drive the car more often or ensure that your piston rings are not worn.

I wouldn't worry about it, unless it smokes for an excessive amount of time while driving. A small puff of oil smoke during start up is a side effect of the horizontally opposed cylinder engine design.

964enthus

only one reply for 98 views so far !!
maybe more over the week end ?

964enthus

oil does damage the cat,read below:

"...Athough every effort is made to ensure our catalytic converters will not fail, sometimes a problem with the vehicle will cause them to break down. The following problems are NOT covered by our guarantee:

Oil Fouled
This is caused by oil getting into the exhaust system and contaminating the catalytic converter. The most likely cause is a leaking gasket...."

Each time you see this white smoke at start up,you know your cat is damaged

darth

white smoke which dissapates quickly likely condensation in the exhaust, blue smoke which lingers likely oil in the exhaust or combustion chamber

jimq

my previous 911'sall did it but for some reason I have never seen it from my 964. Even my TT occasionally will smoke for a couple seconds after sitting for a week or 2.