John McM

My car occasionally smokes on start-up. Nothing to worry about, as it's only on start-up, but I've started to sense that smoking is more predominant when the oil level is either high [after a service], or low. Any techies out there that could hazard a guess whether there should be a correlation between tank oil level and smoke on start-up?

Adrian

If the oil system is overfilled (very common) the engine will smoke on start up until it is has regained its "natural level". This is a dry sumped engine issue. It is also a good idea to remember how to fill the oil and how to check the oil level properly. The most common error during service is to drain the oil and fill it up again with the full capacity figure rather than remembering that you cannot drain 2 litres of what is called unusable oil which remains in the engine unless the engine is removed and split apart.
Ciao,
Adrian
964C4

L8Apex

Adrian,

Why/ how does this happen? (Smoke on start up)

Thanks.

Wet1

I always "fill" mine so it's on the bottom of the dipstick. I used to have smoking issues when I filled it to the full line, I haven't had any issues since I started running it at the lower level.

bogey1

could be a turbo on its last legs as well?

John McM

L8 Apex, the theory [not mine, I'm an amateur here] is that the 964 bore shapes are specifically designed to cope with large temperature variances in the head, typical of air-cooled motors, hence they have larger ring to cyclinder head gaps than water cooled engines, when cold i.e. first start-up [seems to be corrobated by the advice to not rely on static compression checks to see if an engine is good].

Couple the bore shape with the horizontal cylinder position and it's more likely on these engines than others that a little oil will seep into the combustion chamber after close-down and stay there until it's ejected as smoke at start-up.

Bogey 1, if it was constantly smoking and/or blowing smoke on boost I'd suspect rings or the turbo. The thing that intrigues me is that there seems to be a sweet spot in the tank level that rarely if ever smokes on start-up. I can't think of a reason for that, so I'm hoping that someone more technical has worked it out.

Adrian

Dear L8Apex,
John has sort of answered the first part of the question. Because the engine is horizontal and the pistons and cylinders are effectively the bootom of the engine oil will drain downwards. It gets past the rings and that is what causes the smoke.
Now the natural level of oil in a dry sumped engine follows the same principle. If you have too much oil in the system more than the 2 litres unusable will remain in the engine because the scavenge pump cannot draw out all the oil before the engine is shut down.
This excess oil is what escapes past the rings. The same smoke issue occurs if you park the 911 with the nose pointing upwards or at any incline angle like we often have to here in Switzerland. Not much flat ground.
It is not that technical. Dry sumped means oil stored outside the engine. If there is too much oil not all of it can be removed from the engine and then gravity takes over.
Ciao,
Adrian
964C4

Jacks911

Adian,

Would this also apply to oil seapage, Driping a bit in the garage after several days? My 91 ran well and was dry underneath and made a 1100 mile trip using only about a half qt. But since it was now down below the bottom of the dip stick I added a qt. Now it is dripping a bit if it is not driven everyday and the oil level is near the top of the guage & dip stick.

John McM

Just read my Father's Day gift, a Porsche GT Magazine. This edition had a buyers guide to the 964 Turbo and says that some smoke on start up is because the KKK turbos are known to pool oil after shutdown. The article says it's a normal thing for these cars to do so nothing to worry about. Just thought I'd pass that info on, as I don't think I've ever heard that fact, either on this forum or anywhere else.

Sameer

My oil level is usualy filled till slight over the half mark line and yes i does only sometimes smoke on startup for like 2 seconds, nothing more.