I have a 302 that has about 100,000 miles on it. When the car is started cold the oil pressure is in the normal range. as the car heats up the oil pressure will drop to the bottom of the oil pressure gauge at idle but will increase into the normal range between 900 and 1100 rpm, the longer it is ran the higher you have to rev it to get normal oil pressure. The engine does not leek or use any oil and it still runs stong and smooth except for this problem. does anybody know what could the problem could be?