Having issues with the oil pressure in my 1970 350 cu in finally on the road after a complete body and interior restoration. Engine was rebuilt years ago but has virtually no miles on it. Bored 30 over, new pistons, cam, crank, timing gears and high pressure oil pump. Had to change the rear main seal because it was leaking. (of course found this out after putting the motor in) No leaks now. Oil pressure on start-up would go to 50lbs at idle and pretty much stay there until the engine warmed up. Went out driving one day and lost pressure. Down to about 5 lbs. When the engine was rebuilt a high pressure pump was added. So I thought there was something wrong with the pump assembly. Bought and installed a new high pressure kit from T.A. Performance. Pressure on start-up only about 25lbs. With increased RPM's the pressure went down instead of up. Okay, so maybe I am not great at rebuilding a pump so I bought a new timing cover with HP Pump factory installed by T.A. Performance ($450) and spent a whole day tearing the front off of my motor and installing the new. No change!! The start up pressure at idle is about 25 to 30lbs. Increased RPM lowers the pressure instead of raising it. Anybody got any ideas before I yank the motor (and my hair) out and send it back to the machine shop??

 

Did you check if you have a sticking or defective pressure regulating valve?

 

Thanks Hanky. Actually I did. The pressure regulating valve and bypass valve are all clear and appear to be functioning. On someone else s advice I am going to drop the oil pan and verify the pick tube is not sucking air. Since it has pressure a idle and loses it at higher RPM it seams likely that it might be drawing air in the pump somehow. I got my fingers crossed!!

 

You would not believe what I found when I dropped the oil pan a second time. Found parts of an old shop rag had been sucked into the oil pickup. After cleaning it out, everything is great. Start up pressures are at 80lbs or better and normal pressure after warm up is between 40-60lbs. I have put about a thousand miles on the engine with no issues. The rag must have been left in the valley during the original rebuild. Boy was I lucky it didn't wreck the engine.

 

Glad you found the problem, but if it were me, I would drop that pan one more time and make sure the rest of that shop rag isn't waiting to get in there. What do you think?

 

The pressure regulating valve and bypass valve are all clear and appear to be functioning. On someone else s advice I am going to drop the oil pan and verify the pick tube is not sucking air. Since it has pressure a idle and loses it at higher RPM it seams likely that it might be drawing air in the pump somehow. I got my fingers crossed!!