[ainarssems]

Originally Posted by SyncroS8

Crankcase pressure is sucked out due to being connected to the inlet system.

Put too much oil in and there's less room for the air to move around hence the pressure build up.

To give you an idea of how much pressure there is, we use vacuum pumps on race engines which gains more hp.

MG

When you explain it like that it kind of makes sense. The pressure in crankcase is not constant but pulsing as pistons go up and down. If there is less room it cannot swallow pulses that good and peak pressure at the top of pulse is higher and lower at the bottom of pulse making greater difference in max and min pressure. I can see how this could effect seals. This would also have more effect with low number of cylinders and less with higher number of cylinders I guess.