too much crank case pressure...., how can you tell? Options

[jr91472]

So a little history. I am struggling with a rear main seal that doesn't want to stop leaking oil (sounds like I am not the only one).

I am down to two possibilities (that I know of)
1. excessive wear on the flywheel hub
2. excessive case pressure

Focusing on #2, how can you determine if there is too much pressure?

One mechanic told me that one test is to simply place the oil filler cap on the oil fill neck (without tighting) while the car is idling. If the cap blows off = too much pressure. Anyone heard of this?

Ultimately, what is the cause of excessive case pressure? and how do you fix it?

sorry for all the newbie questions, but these things keep me awake at nite......

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[Jakester]

I'm far from the resident engine guru around here (we've got plenty of those), but since noone else is chiming in, I'll offer my advice.

Crankcase pressure is a by-product of blow-by; that is, pressure from the combustion chamber "blowing by" the piston rings and pressurizing the area under the pistons - the crankcase.

If you have oil spewing from many different gasketed surfaces in the region of the crankcase, that's an indication of excessive crankcase pressure and thereby blow-by. It's usually a bad juju type of sign, since the only fix (outside of motor honey and quick sale) is an engine rebuild.

A normally running engine shouldn't have a lot of discernable flow of "air" out of the oil fill cap, but I'm not familiar with test methods or the specifics of the type IV motors.

P.S. Some crankcase pressure (i.e. blowby) is normal - a compression test will tell you how bad your blowby is, assuming your valve sealing is good.