That is a good question. The official explanation says that the valve opens as pressure builds up and the rod sprayers emit a stream of oil at the dippers. It must allow some at low pressure to keep the dipper trays supplied.
You were saying before that you had zero oil pressure. If you have zero pressure above idle that there is a problem and it won't run for long like that. Sometimes if the distributor is not bottomed all the way, the oil pump will not turn. With the distributor removed you can drive the pump with a drill and see if you have pressure.
Last edited by truckernix; 08/24/2010 8:05 PM.
