Re: leakage at oil filler cap - Saab Vintage Models Bulletin Board - Saabnet.com
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Re: leakage at oil filler cap
Posted by kansas (more from kansas) on Sat, 24 Nov 2012 10:59:51
In Reply to: leakage at oil filler cap, -jsaxcski2, Fri, 23 Nov 2012 15:16:33
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AFAIK the crankcase and valve train are open to atmosphere on all V4s through the oil filler cap (unlike modern engines which have sealing oil filler caps). Leakage at the cap would mean oil is being pushed out by pressure in the crankcase. Pressure in the crankcase comes from ring blowby. It is normally countered by the PVC system which connects the crankcase through the PCV valve to the intake manifold, resulting in slight vacuum in the crankcase to pull vapors into the cylinders. (Older, pre-PCV engines simply exhausted crankcase vapors to atmosphere.) There is likely a diagram of system operation in your manual.
So I think you have too much blowby to be controlled by the PCV system (worn or stuck rings, etc), or (preferably) incorrect PCV operation (defective hose, stuck valve).
You can see if the crankcase has pressure or vacuum by putting a piece of heavy paper, like a business card, over the oil filler opening at idle and when revving the engine.
Sealing the filler opening would simply result in the excess pressure blowing out the dipstick tube. Sealing both would result in oil being forced past the crank and balance shaft seals.
posted by 75.147.23...
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