Particularly on a cold engine with thick oil, the relief valve will operate pretty continuously. For oil pressure to build up at all, more oil must be supplied to the bearing than can be leaked away. If we supply one drop of oil to the bearing for every one that leaks out the side, the pressure would be zero, but the bearing wouls still be lubed properly. Bearing damage happens when we supply LESS oil than is being leaked. Once the parts, and the oil get hot, there's much less need for pressure relief. That's why cold engines with thick oil have high oil pressure.
If it were possible to maintain only one pound of pressure, consistently, under all operating conditions, the bearings would never be damaged and there would be no power loss from building up excess pressure. Since that's not practical, a little over-capacity is built into the pump, and the relief valve is there to keep the pump from operating in a hydraulic-lock situation.
Jerry
