Pressure testing oil galleries is a difficult, complicated process and is usually done on a bare block after a thorough cleaning. It's necessary to plug as many leak points as possible, such as main bearing oil holes, etc. I use a piece of gasket material sandwiched between the crankshaft main bearing journals and the block and a few other sneaky tricks, then apply 50-75 PSI air pressure to the system, fill the block with water, and look/listen for leaks in the cooling passages. I don't know of a simpler method to find that kind of a leak.
Jerry
