NEED HELP LOW PRESURE
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Senior User
Joined: Sep 2002
Posts: 107
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From: home
NEED HELP LOW PRESURE
My friend has a 70 F250 camper pecial with a 390 and 4spd he has low oil presure and the local shop said it is a bad oil pump. He has 40 weight oil and when it is cold it has great presure along with high RPM. We would like more opinions on the problem.
Fleet Mechanic
Joined: Jul 1999
Posts: 1,360
Likes: 1
From: Iowa
NEED HELP LOW PRESURE
My old '70 F100 had low oil pressure. 22lbs hot at 2500prm, and 0psi at hot idle. I replaced the rod and main bearings, along with the oil pump and the oil pump driveshaft. Now I've got 15lbs@ hot idle, and 40spi at 2500rpm.
Senior User
Joined: Aug 2002
Posts: 101
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From: Bowling Green, Ohio
NEED HELP LOW PRESURE
The rule of thumb for oil pressure I have seen (and use myself) is 10 psi for every 1,000 RPMs when warm. Everything has decent oil pressure when it's cold. So, you would want about 6 or 8 psi at
hot idle (depending upon where your idle is set). Usually low oil pressure is a sign that your bearings are worn. My old 68 F100 had low oil pressure and I tried to fix it by replacing the oil pump (but not the bearings). I probably gained 1 or 2 psi...total. I ended up rebuilding the engine. If you have low oil pressure, odds are replacing the oil pump will not improve your situation.
Ohio Bill
hot idle (depending upon where your idle is set). Usually low oil pressure is a sign that your bearings are worn. My old 68 F100 had low oil pressure and I tried to fix it by replacing the oil pump (but not the bearings). I probably gained 1 or 2 psi...total. I ended up rebuilding the engine. If you have low oil pressure, odds are replacing the oil pump will not improve your situation.
Ohio Bill
Cargo Master
Joined: Aug 2000
Posts: 2,931
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From: SW Michigan
NEED HELP LOW PRESURE
Your local shop doesn't know they are talking about. Oil pumps rarely, if ever, go 'bad'. The oil pump is doing fine, as evedenced by the good pressure when the engine is cold. As the engine gets warm, the oil gets thinner, and the pressure drops. This is more noticeable in an older engine with lots of wear on the bearings. If the engine runs well, and the bearings are quiet, you can leave them alone. It is MUCH easier to get some more pressure by putting in a Mellings M57HV oil pump. Even though your oil pump is not 'bad' the high volume pump will push about 20% more oil through the same clearance, thus raising the pressure. You might also want to put some restrictors under the rockershafts. And how about some 20-50 oil ? DF
