The oil pressure relief valve was stuck open causing the low oil pressure. I removed the solder joint on the valve and extracted the spring and piston. The piston was stuck and the spring was compressed in its center. Photo of the parts after extraction is here:


I am going to do the modification laid out by Tiger Tom to make the spring tension variable.

A few questions:
Does anyone know the specs for the spring – what length it should be and how much force it should normally provide?

I’d like to test the modified PRV to get it within a reasonable spec prior to installing it on the car and testing it out. At what oil pressure psi should the relief valve open up to allow the oil to flow through the by-pass vent holes? Is it around 40 psi?