My uncle has a 66 GTO with a 400 motor in it. The person he bought it from said that he overhauled engine and put 500 miles in it. My uncle put another 150 miles on it. He changed the oil this weekend taking out the break in oil and putting in 10-40 oil. When first starts it runs 75 lbs of oil pressure but once engine gets warm it is between 5 and 10 at idle. When cruising down the road it runs 15 lbs of pressure @ 2000 rpm's Is this normal or is something wrong??
I've been told by several old time Pontiac guys that as long as you get 10psi of oil pressure per 1k rpm the engine is fine. So, if the car is idling at 1k rpm and you have 10psi oil pressure, rev the engine and hold it at 3k rpm and see if it holds 30psi of oil pressure etc...
Thats to big a diff.if the valves dont clack you may wanna ck the valve adjustment.to make sure that thay have not been bottomed out in the lifter its a trick people use to hide in a engine that has low oil pressure most likly you have to clearance in the main and rod bearings..if the lifters have been bottomed out you have u have alot more problems cam n lifters...if not motor out turned crankshaft new bearing-and u can get a 80 psi oil pump normal oil press on a rebuilt engine should be 30-40psi at 2000rpm if not its not been built checking clearance.And the oil press in a pontiac is at the rear main bearing gallery oil has to travel though the rest of the engine and engine is not have enough supply of oil .seen it many times my press cold 80 psi- hot2000rpm 60psi-idle 35psi..30 year Pontiac man...