oil pressure way high

Just bought a 99 XJ Sport, 51K miles I6 4.0 4WD

Oil pressure normaly runs at about 40 at idle 900rpm tehn goes to about 55-60 at 2K rpm. Last night I got in it let it warm up for 10 minutes or so. The oil pressure went right to 40 at startup and after about 10 seconds ran all teh way over to the full right end..pegged at 80 never did go down or fluctuate at all for the 5 minutes it takes me to drive home. I shut it down and started it back up same deal. It was about 28 degrees last night jeep was at about 200Degrees prior to moving. Whats the problem?

did you check the oil? Or change the oil. Could have to much in there. Just a thought. Or the sending unit might be bad.

I'd like to second the sending unit. Both of mine do the same thing, occasionally peg the gauge. Even the other XJ I owned sometimes gave random oil pressure readings. I doubt the sending unit costs very much, if it gives you any more grief, just replace it.

Jared

Oil Pressure Sending Unit

DeadEyeJ said:

I'd like to second the sending unit. Both of mine do the same thing, occasionally peg the gauge. Even the other XJ I owned sometimes gave random oil pressure readings. I doubt the sending unit costs very much, if it gives you any more grief, just replace it.

Jared

Click to expand...

My XJ had the same problem twice, checked oil pressure with a guage and read within normal range changed the Sending unit which was 6 and change. and problem was fixed

Make sure the sending unit is properly connected, then if it is, assume that it's dead. The later (91-up) senders will pin the gauge when disconnected or broken.

Thanks

Thanks for the input guys. I haven't changed the oil. Checked it and it didn't read over full. Today the needle did jump around a few times before it would peg, which backs you guys up in questioning the sending unit, it wasn't doing that yesterday just pegged. Just out of idle curiosity what are the normal operating pressures for the 99? I searched and found a post about a 92 that gives 13 psi at idle and 75 max at 2K plus, mine has always "Indicated" way higher than that.

think of the gauge as a general guideline.

they are NOT accurate!

You can test the guage easily to determine if the guage is bad or the sending unit. All you have to do is this:
Inplug the connector from the sending unit and look ar the guage, it should be pegged. Then take a short piece of wire and ground the connector, the guage should go to zero. It will do this because the sending unit measures resistance so if there is no connection there is infinite resistance. When grounded there is none.