[billnorman]

There is a little goodie in the oil pump called a Pressure Relief valve. It's supposed to hold a ball tight to the oil pump outlet unless the pressure (in a cold motor) exceeds a pre-set value usually 30 pounds. At normal temperatures it still vents this pressure at 30 PSI but a hot oil develops much less pressure so it bleeds less oil off. If this check valve gets any trash in it, or the spring breaks, or weakens or the ball sticks, your oil pressure will be really low when the motor warms up. One way to check this is inspect the oil pump. Remove any trash etc. One other way to fix this (don't try this at home) is hammer a cold motor and try to flush out any stuck stuff with high oil flow. Don't blame me if it blows up.