The oil pressure of an engine is established by the clearances that exist in the engine (bearings/galleries/etc). Oil pressure is affected by oil viscosity, oil pump efficiency, oil supply, temperature, and the oil pump relief valve.
I recommend starting with the easiest things first......OIL SUPPLY, then install a new gage at any access point in the output side of the pump (block) and check the readings. Oil pressure should remain relatively constant once the engine reaches operating temperatures,with only slight increase as RPM's are increased. If the same high irratic condition is found using a new gauge you have an internal engine problem. Start again with the easiest....the oil filter (if equipted) the new spin on filters actually has a relief bypass built inside the housing and may be malfunctioning. Next check for ample flow of oil at the rocker shaft assembly, make sure the system lines shaft etc are not clogged up causing excess back pressure. Next the pump and relief valve assembly, clean, inspect, and replace if found worn. Finally, the bearings, mains, rods and cam shaft........yikes I hope you don't get this far!(these are NOT likely) as bearing surfaces wear, the restrictions (space for oil flow within the engine widens) and oil pressure dcreases (usually in worn engines). Most likely something is plugged up somewhere!!
