Gary Christensen

93 Cherokee 4.0 high output
oil pressure is almost at 80 when starting and has been going down to about 60 or a little below after driving around. Any ideas? Also is it bad to drive around like that?

TrailerTrash

Verify the pressure with a mechanical gauge or a pressure tester

country2

Normal, cold oil is thicker hence higher pressure as it heats up gets thinner so could drop some. Mine cold is 75 at temp going 60 down road its around 60 and my idle is low at 9 psi. "Think" spec wise is idle is no less than 11 psi and 10 psi per each 1k rpm.

tjwalker

It is possible that your oil pressure sending unit might be a little off. Should definitely come down from 60 psi at idle, closer to 20 psi at HOT idle give or take a few psi. But if it is at 60 psi with a hot engine going down the road at a higher rpm, that is just fine with no worries. (see oil pressure spec below)

So you know, oil pressure sending units are a very common failure on the 4.0 engine.

You can verify true oil pressure with a mechanical gauge as TrailerTrash mentioned (can be rented from parts stores), or just live with it, or get a replacement and install it if readings are verified to be too high on your dash gauge. If you replace the oil pressure sending unit, I highly recommend getting a Mopar unit from Jeep for best reliability/accuracy/mating with your factory gauge.

By the way, here is the oil pressure spec for the 4.0 engine:

*Not less than 13 psi at HOT idle

*Between 37-75 over 1600 rpms

country2

Guess I misread it... your saying basically its staying between 60-80psi and never going to 0psi when off?

Gary Christensen

Thank you everyone. It was the sending unit. Quick and easy fix!
sits at 40 now while driving