318 low oil pressure

01-08-2004, 02:52 PM
I have an '85 D250 full size pick up with 318 engine. At 2000 RPM, my oil pressure is 20 psi. At idle it is nearly zero. My manual indicates that I should have at least 30 psi at 2000 RPM, and I am concerned that this engine wil not last very long in its current state.

I recently freshened up the engine with new main and rod bearings, rings, and a new standard oil pump, among other things. Main and rod bearing clearances were all between .0015" and .002". Before I did that work, the oil pressure was about the same as it is now, or possibily a little higher.

I'm running 10W -40 oil.

I have comfirmed the oil pressure reading with another gauge. The two gauges are in agreement.

When I did the engine work, I discovered parts of the old valve guide seals in the oil pan and the oil pump pick up. I thoroughly cleaned the pan, oil pick up tube and screen before I reassembled everything.

I have done a lot of engine rebuilds in the past, with good success, but this was the first time I have been inside of a 318 engine.

If I remember correctly, the oil pressure releif valve is in the oil pump itself. Since I installed a new oil pump, I don't think that it is the problem.

I'm reluctant to try to put a band-aid on the problem by installing a heavy duty oil pump. I'm not sure how much good that would do anyway. I would prefer to get to the root cause and fix that, even if it means pulling the engine again.

I would be grateful for any suggestions from the group.

Michael Foote
02-26-2004, 10:57 PM
If you are using the electric gauges for your test install the kind that is not electric.

02-27-2004, 07:55 AM
Thanks for the reply. The aftermarket oil pressure gauge on my dash and the one I was using to confirm its accuracy are both mechanical gauges. I have a high level of confidence in the mechanical gauge I used to test the dash gauge.

One additional piece of information: The oil pressure is up around 40 psi or more for a couple of miles when the engine is cold. After it warms up, the pressure drops back to 20 psi at 2,000 rpm and nothing at idle.

Michael Foote
02-27-2004, 09:25 AM
I'm not a mechanic professionally but in my 318 I'm afraid I'm going to find out that it's the oil pump. The engine runs fine and is tight as a drum, but at 250,000 mi. I figure it's the only possabillity. And with the newer engines there could be a fault in the parts of yours. But again I'm not a mechanic, but replacing the pump on yours and have it not be the problem is cheaper than an engine if it is. I have read in other threads that it could be a relief valve but in a D250 truck I would have used a heavy duty pump. Maybe you should talk to a good machine shop and pay them to pick their brain.

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