What causes an oil pressure drop from 35 lbs cold to about 10 lbs when the engine gets up to running temp? Have been running 10W40 in it and noticed the pressure was not very high on the old oil gauge, so I put a new gauge on it. Pressure dropped to about 10 lbs on the new gauge. Today I tried running straight SAE 30, and the same thing is happening. New filter and gasket, no leaks and I did check the oil hole in the bottom of the filter bolt, that is not clogged. Also, no hydraulic oil is leaking into the engine oil. Any ideas what my problem may be coming from? Ten pounds of pressure does not seem adequate to me or is it acceptable in these engines?