[diveplane]

Originally Posted by xs-style

1990 Silverado
350 gmp crate motor with 30k

New oil pump and screen
New oil pressure switch
Fresh oil and filter
Replaced one quart with Lucus stabilizer

The oil pressure is way inconsistent.

First start up after the swap it sat and idled smooth with a gauge reading of 40 psi till warm then dropped to 20, still running smoothly.

Let it sit overnight cuz it was late.

Crunk up again this morning, same result. Oil pressure holding steady about 30, engine running smoothly....all appears well.

Everything seems fine, so off to the end of the road. My road is only about a mile to the end, and I got up to about 45. That had the gauge reading at about 35. Seemed good.
So I decided to drive a loop around the neighborhood. It's maybe a 3-5 mile round trip. About halfway through the round the oil pressure dropped to zero again. Then it jumped back up. I spent the next 2 miles of the trip watching the pressure float between zero and 25 on the gauge, and feeling the truck start run rougher.

Got it back home and let it (and me....) chill. After an hour or so I went out and fired it up again. Pressure went to 30 for a few seconds then dropped to about 15. If I rev it a little I can be in the pressure up, but it's still running rough.

With a new pump, screen, switch, and fresh fluids... what's left?

Ps: checked the can bearing while I had the pan off. no play in the rods to speak of.

oil pressure sending unit? , or dash temp stepper motor?.