Jakejones514

Hi I have a 93 f150 with the 351w in it. All of a sudden it loses oil pressure once the oil warms up. I've checked it with a mechanical gague and it's not a sender or electrical issue its actually losing pressure, however it doesn't knock or run any differently when the oil pressure drops. The oil pressure is only low at idle as well. I rebuilt the bottom end completely from the oil pickup tube to the main bearings and the problem is still there. Anyone know what is causing this? The oil is not contaminated or anything I am seriously stumped here.

88xlt

What exactly does the mechanical gauge read when your engine is warmed up at idle?

Jakejones514

It starts out at about 55 then gradually drops to about 3 to 4 psi

88xlt

3 to 4 psi at idle should get you by, especially if you don't let it idle for any length of time at once.

As far as what is causing the low oil pressure, it's very hard to patch up an engine from the bottom end(I assume that's what you did, without removing the engine?). To fix an engine properly you have to pull the engine, mike the crankshaft, and/or plastigage the bearings, etc.

My advice just live with it and take care of it best you can, maybe use a little thicker oil, and it may well last you a very long time. When and if it does fail remove the engine and rebuild it properly if you wish to keep the truck.

I have used a lot of less than perfect engines and have had very few complete failures. Best of luck.

Jakejones514

I did pull the engine. I didn't remove the crank entirely but I took all the bolts on it off and was able to slide the new main bearings in. I plastiguaged them after the new ones were installed and the clearance was in spec that's why I'm so confused. Maybe the oil pump I was sold was a rebuilt one and isn't good that's the only thing I'm thinking could cause this problem

Chris_1

iTrader: (1)

The way you did it is not the same as pulling the crank, having it miced and polished and turned if necessary and having the rods resized and all new bearings. That would give you nice, normal oil pressure.
Just slipping in some new main bearings is a temporary measure that may get you by for a while, but it is not the same as redoing the bottom end. You can sometimes get away with what you did and quite often not.
So to say that you're lucky it even runs isn't to be nasty - quite honestly, you're lucky it even runs.

Jakejones514

The problem I'm having is not with clearances. I have checked all of the main bearing clearances multiple times. The surface of the crank is perfectly smooth everywhere. The engine runs perfectly I just don't like seeing the oil pressure down at 3 psi.