dragonflyXJ

I recently did a full head and motor swap on my 91 XJ.

Everything was cleaned, machined and checked out by one of the top shops in the country for this kind of work.

Prior to swap I had no oil pressure issues.

Now, even after completing the re-seating and break in procedures I am having high oil pressure at start up.

If she has sat over night, even if its warm, she starts at 70-80 and comes down to normal operating pressure over the course of 15 minutes of idling.

Once down to normal, no issues are encountered while driving and if I turn her off and don't let her set longer than an hour or so she starts up at normal pressure.

Where should I begin with trying to diagnose this? Sensor?

Thanks in advance!

tjwalker

The primary suspect here is the oil pressure sending unit, located directly above the oil filter.

If your XJ were at a shop, they would remove the sending unit and temporarily install a "mechanical oil pressure gauge" where the sending unit resides. Doing that will give you an oil pressure reading you can believe.

If oil pressure with the mechanical sending unit is acceptable, then the oil pressure sending unit needs to be replaced. Preferably with a MOPAR unit purchased directly from Jeep. The MOPAR sending unit will give you the best accuracy/reliability/mating with your factory gauge.

Good luck and keeep us updated!

dragonflyXJ

Also has a follow-up I'm out here ****ing around and realized I didn't mention that it is a 95 engine that we put in but we still have the original 91 oil pressure sending unit mounted.

Could that crossover be causing issues?

dragonflyXJ

Thanks man! Ill make some calls to shops tomorrow!

Turbo X_J

I didn't know Lingenfelter did Jeep engines?

Don't really need to call a shop just grab a cheap OP gauge from Amazon or Vatozone.

dragonflyXJ

Didn't realize they'd be that affordable.

Ray's cracked heads in Seymour, he has racing guys sending him heads from as far out as Cali on a weekly basis.

dragonflyXJ

Just finished replacing the oil sending unit, still sitting at 80 on startup :/

fb97xj1

Is it a Mopar sending unit? And is that 80psi reading off the dash gauge, or is that from a mechanical?

BlueRidgeMark

I got a Bosch for under $20 at Pep Boys. It took all of 10 minutes to connect it, set the gauge on the cowling where I could see it, fire up the engine, get a reading, and put back the old sending unit.

I keep the Bosch around strictly as a test unit.

dragonflyXJ

Reading reading off the dash, don't have a mechanical but am headed back out to get a kit.

I was told on another Forum to unplug the sending unit and see if the pressure drops to zero while the engine is on, when I did that the pressure went even higher past 80.

BlueRidgeMark

You could have a wiring problem to the sending unit. The mechanical gauge will tell the story, and you'll know where to go from there.

s346k

definitely check any oil pressure concern with a mechanical gauge asap.

what weight oil and what’s the ambient temp? ive owned several vehicles that made 70+ psi cold and 35 warm at idle. it’s not terribly out of the norm. what kind of oil pump?

i can see a fresh rebuild doing that. my 245k motor still makes 60/30 on stock everything with 5w30 dino oil in it.

Thernlund