The Oil Pump Pressure Relief Valve, located at the bottom of L-Series oil pumps, is one of two relief valves that help regulate oil pressure (the other is located behind the oil filter: 17-8041). L-Series oil pumps always push the same volume of oil each rotation, which is how oil pressure is increased at higher RPM. The pressure relief valves work together to ensure that too much oil is not being pushed through the system (and out of the seals if it gets high enough!). If you start seeing abnormally high oil pressure, checking these two valves for proper operation first can save time and money.
Datsun 240Z, 260Z, 280Z, 280ZX
Datsun S30, S130
1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1982, 1983