I've read several threads regarding overfill, some attributed to blowing an engine. What is the mechanism of failure in the 996tt engine? Not really very familiar with this dry sump engine, but I had an old Beechcraft Bonanza that was also a dry sump boxer engine, albeit air-cooled, but the biggest problem with that was that at altitude it would foam and blow out the top and cover the engine compartment.

 

In a dry sump system the tank has vents, some vent to the motor to equalize the pressure and allow the oil to flow without vacuum creating a problem. Overfilling can displace clear air passages with oil. Also oil can overfill the crankcase to the point that pistons will try to push through oil on their underside leading to rod and other mechanical failures. My info is general and not specific to the 996T as I've not studied the oiling system.

 

The concern is the over filling reduces the amount of space there is for the oil vapor to be removed from the crankcase fumes and the efficiency of removing the oil from the vapor is reduced.

The result is more oil -- in the form of vapor -- gets routed to the engine where is it burned.

Oil in the combustion chamber negatively affects the ability of the gasoline to resist detonation thus under hard acceleration this could be more likely to occur. Sure the DME will detect this via the knock sensors before it becomes a real threat to the engine and back off timing and maybe reduce boost (or the timing being backed off has this side effect) but the bottom line is the engine makes less power due to the oil vapor in the intake charge.

There is the concern about engine deposit build up, too.

Might add in severe cases of overfilling there is the risk of oil from the vapor wetting the intake walls then upon engine shut off this oil draining down into the engine, into a combustion chamber if the intake valves are open, or collecting on top of the intake valves if they are closed.

(This happens as we sometimes see the cold engine making some smoke upon startup. This comes from oil that has collected on top of the intake valves or has managed to get into the cylinder via open intake valves.)

Upon engine start this oil could be enough to result in a hydraulic lock up of the engine.

There is no excuse to overfilling one of these engines with oil other than the person who did this doesn't know what he is doing and shouldn't be allowed near a Turbo engine (or any engine).

OTOH, there is no real reason to under fill these engines either. Fill the engine to the max line and keep it there, with reasonably spaced or scheduled or timed top ups if the oil level drops over time, and it can.

Keeping the engine full of oil maximizes the volume of oil in the oil tank the oil pump has at its disposal to supply the engine with oil under all operating conditions.

Keeping the engine full of oil maximizes the amount of additives to combat the effects of oil contamination.

Keeping the engine full of oil maximizes the amount of oil there is to share the burden of carrying away heat from the hottest parts of the engine.

 

Good info and at the least can cause excessive smoke.

 

When too much engine oil fills the crankshaft in your car, the oil becomes aerated and is whipped into foam. This is caused by the high rotation of the crankshaft. Foamy oil cannot lubricate your car well, and in many cases it will cause oil flow to halt completely, overheating your oil and causing loss of oil pressure. The engine then becomes starved for lubrication and may potentially lock up.

 

Is yours a '99?