The rule of thumb is at least 10 psi per 1000 RPM. You need a mechanical gauge temporarily installed into the location of the original sending unit. This can be tapped in with a "T" fitting. Run the gauge tubing into the car so that you can get a true pressure reading in PSI while driving.
If the pressure reading is lower than the 10 psi per 1000 RPM, you either have an engine with too much bearing clearance, an oil pump problem, (weak relief valve spring, pump clearances too great, pump pick up too close to the bottom of the pan- it needs to be 3/8-1/2 inch from bottom of oil pan, pick up not sealed to pump or pump not sealed to block, or a clogged pick up screen, due to excessive use of silicone gasket sealer that has broken loose and settled into bottom of pan).
Without a true reading in PSI, you really don't have much to go on. I don't trust an electrical oil pressure gauge for a true reading. It's OK for use as a reference after verifying the needle position with the true amount of pressure. An engine with 500 miles on it shouldn't be showing too much variation in pressure after warm up unless the bearing clearances were set on the loose side. Was this engine's bearings and bearing surfaces renewed when rebuilt?
All engines will show a slight reduction in oil pressure after warm up due to the expansion of the parts and the slight loss of viscosity of the oil, but if you find more than about a 10-15 psi drop across the pressure range, something isn't right. You really need to know what the true pressure is.
If the pressure reading is lower than the 10 psi per 1000 RPM, you either have an engine with too much bearing clearance, an oil pump problem, (weak relief valve spring, pump clearances too great, pump pick up too close to the bottom of the pan- it needs to be 3/8-1/2 inch from bottom of oil pan, pick up not sealed to pump or pump not sealed to block, or a clogged pick up screen, due to excessive use of silicone gasket sealer that has broken loose and settled into bottom of pan).
Without a true reading in PSI, you really don't have much to go on. I don't trust an electrical oil pressure gauge for a true reading. It's OK for use as a reference after verifying the needle position with the true amount of pressure. An engine with 500 miles on it shouldn't be showing too much variation in pressure after warm up unless the bearing clearances were set on the loose side. Was this engine's bearings and bearing surfaces renewed when rebuilt?
All engines will show a slight reduction in oil pressure after warm up due to the expansion of the parts and the slight loss of viscosity of the oil, but if you find more than about a 10-15 psi drop across the pressure range, something isn't right. You really need to know what the true pressure is.
