Quote:
Originally Posted by big2bird
Why. It's broken. Out it comes.
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If he has a defective or plugged PCV system, it can cause excessive crankcase pressure.
Also, a leakdown test can help pinpoint where he is losing compression and exactly how much.
If he can clearly hear a whooshing/howling by listening at the oil filler cap during the leakdown test, he's losing compression through the rings.
If he can hear it (or even feel puffs on his hand) at the tail pipe, then it's his exhaust valve on that cylinder.
If he can clearly hear a whooshing/howling by listening at the carb/intake manifold, then it's his intake valve on that cylinder.
If he can see it bubbling in the radiator, it could be a head gasket, although it doesn't sound like that's it.