Inliners International Forums General Discussion Engines Oil pressure too high? GMC 270

I have about 1000 miles on this engine since putting new bearings, crank grind and new cam in. I am using the exact same oil pump as I did before this work but now my oil pressure is quite a bit higher than it was before. The motor had about 20,000 miles on it and the crankshaft broke which is why I redid bearings, crank, cam, etc.

I started out running a bronze distributor gear and when I checked it after 1000 miles - it had considerable wear.

I replaced it with a cast gear that was in good condition.




I am looking for feedback on whether I need to pull the pump and see if the pressure relief valve is somehow out of adjustment (are they adjustable?).

When it is cold, it pegs the oil pressure gauge and when warm, runs about 40 - 45 psi at idle and pegs it at anything above 2000 . . . running Delo 15W-40

It was suggested to add another oil pressure gauge to verify that mine was accurate and other than the new gauge being a lot slower responding, the new gauge does indicate that the pressure is higher than the in dash gauge can show.

Here is a video of a cold start and oil pressure.

I also run 15/40. My wagon with 250 runs real high oil pressure. I calmed it down by using 10/30 and some GM EOS additive for the cam.

I am going to drop the pan and compare the pressure relief spring and components with a spare pump I have laying around. I would prefer to see a high pressure mark of something less than 60 psi for reduced wear on the cam/distributor gear and peace of mind.

It sounds healthy though! lol I agree with whats been said...Straight 30 or 10-30 should help.

You could save yourself a lot of work, run the cast gear and change the oil to mobil1 (or amszoil)5-30 with a ZDDP additive to get the zinc levels up.

If your bearing clearances are tighter than the old crank the oil pressure will go up. Running a thinner syn. oil will do 2 things:

1) bring the oil pressure down
2) allow more oil to pass through the bearings thus cooling them.

The old adage of running heavy oil - in my opinion - does not hold any value anymore. The shear strength of the syn. is a lot better than the heavy oils without the drag.

The oil pressure relief is a very simple piston that is spring loaded to control oil pressure. If the piston is stuck or jammed from debris it could hang either open or closed. Obviously if it's stuck at a point before it uncovers the relief port the pressure will be to high. Than what happens is the oil in the pump will not circulate out the relief port. This makes high heat in the pump as oil now has to fight massive pressure and leak back past the gears and shafts instead of relieving out the relief port. I would investigate.

This will put lots of strain on the dist drive and cam.

Yes they are adjustable by changing springs or shimming, but I don't believe that to be your issue.

I didn't see if this is a full flow filter conversion or an origonal system? A full flow filter I think will have an internal bypass that will open and bypass the filter when pressure is too high. And this isn't good either. It was meant as a bypass when oil is cold and close under normal conditions.

Frank