I had problems with oil pressure on my 502 MPIs with the Moroso oil pumps so I removed them and installed the stock Mercruiser pumps. I installed a mechanical oil pressure guage at the remote oil filter location by removing one of the unused plugs. The guage shows 45 psi at idle 700 rpm and 60 psi at 1200 rpm. The electric guage on the dash which has a sending unit on the block shows 38 psi at idle and no difference at 1200 rpm. Should there be that much of a difference at the two locations?

Oil pressure does not run to the gauge on the dash it just reads electric impules from the sending unit, the mechanical guage is going to more accurate. all guages can have a 10-15 percent var, if you want to troubleshoot sending unit swap with other motor and read...at higher rpm most gauges tend to read more of the same

Dave
Team Carolina

The sending unit for the dash guage is right above the oil filter adapter plate where the two hoses for the remote oil filter come out.