Oil change crankcase oil

[9sixty4]

How much oil is typically in the crankcase during an oil change? I ask because my experience with a previous 964 was not much at all … less than ˝ quart. In this 964 when I drained the oil there was at least a quart in the crankcase. Is there a “drain back” problem here?

[Walt Fricke]

Jim

I don't know the 964 oil system as well as I do its predecessors, though I think it is basically the same.

In the earlier engines, as a general rule the longer you let the car sit, the more oil ends up in the crankcase sump. The oil in the tank tops out well above the "sump" area of the crank, so gravity is pushing it in that direction. The most obvious sign of this is the oil level in the tank. If you measure the oil level with the dipstick hot, and let it sit overnight, you will find it is a quart or more lower in the tank in the morning. Most of us have overfilled our oil system as a result of such a misleading reading.

I have identified two places where I think oil can leak into the sump:

Out the shafts of the oil pump (these are not sealed, and oil can migrate past the pump gears).
Past the safety pressure relief piston (this is not sealed either, and is fairly low down, and oil can get through the pump gears).

Both are such tight fits that they do their job with the engine running just fine. But oil can still get around these areas,and the less the viscosity and the higher the ambient temperature, the more can get past them.

I used to wonder if the gravity pressure on the oil could cause it to get into bearings and leak out there, but the oil has to go so far up before entering the bearing distribution system that I have given up that theory.

I just make sure I have a pretty large pan for the engine drain no matter what.