My brother just bought the newest member of our family. 91 Yj with 4.0 in it. It runs SUPER cool (enough to get an engine code on it) and the oil pressure is high.

Cool is no biggie, got a new thermostat going in tonight and we'll see if that fixes it.

Oil pressure I dunno though. At idle the guage sits above half, and driving it fluctuates between 3/4 and pinned to the top of the guage. Could it be the guage is off? Bad sensor? Is it something to be worried about?

:beer:

I had a *cough*ricer*cough* one time that the check valve in the oil pump locked up....putting so much pressure into the system that it was blowing the gaskets on the top of the oil filter out along with all its oil... Could try there... I'd suggest new guage first just so you are 100% sure its actually high.

It is probably not the guage. It is usually the sending unit. It is a $15 or so part. Usually when they go pad they pin all the way to the top though. You could always hook a mechanical one up to verify it is reading correctly. My motor runs around 6-10 at idle and close to 40 at high way speed.

This one is over 40 at idle :eek: and between 70-90 I think at about 2500+ rpms.

Where is the sending unit located? Is it a PITA to swap it?

it's right next to the oil filter on the adapter housing.
follow the purple wire

It is real simple to change. I think even you can do it :flipoff2: . I just think it is funny you are asking such a JUish question. Go here (http://www.jeepsunlimited.com) and use the search button. It has been covered a thousand times. :flipoff2: .

On a more serious note. If the previous owner was dumb enough to put a 160* t-stat in the motor he might have hurt the motor. If the 4.0l doesn't get hot enough it runs in "cold start" open loop program. This is a fuel rich program and tends to create heavy carbon deposites on the valves, cylinder walls and plugs. I don't know if this would contribute to the high oil pressure though.

:flipoff2: JU scares me......I am afraid I will get a yeast infection if I stay there too long at a time :laughing:

Interesting note on the temp. I dunno what it has in it, but it runs cool as hell! No oil ANYWHERE on the motor though, clean as a whistle :confused:

Try removing the sending unit and cleaning it and put it back in. My pressure gauge pegged out on me and I cleaned it and it was fine. It does typically fluctuate quite a bit especially as RPMs climb. That is normal. What does the cooling system have in it? You may be able to change fluid to get the temperature up a little. If it is straight water then it will run cooler than antifreeze/water.

might have toomuch oil in it

Originally posted by DE Jeeper

I would think if the motor was actually running at 70psi that it would be blowing oil out of the dip stick.


:eek: Oh my God and I get made fun of!!! How stupid can you be??? :laughing: Blowing oil out of a dipstick due to oil pressure!!! :laughing:

It may be due to the oil being too cold. Get the correct t-stat in and see what happens befoe yo do anything else.
If it still is high, put a mechanical on it & see what it really is. I'd be willing to bet it's the sender.

Originally posted by The Jerk
might have toomuch oil in it

This might be the best suggestion yet. Have you checked the level?

Originally posted by DE Jeeper


This might be the best suggestion yet. Have you checked the level?

Doc, :flipoff2: , the oil pan is pressurized when the motor is running if it is that high it can come out of the dip stick. If you don't think this can happen pull the stick out a little and drive around. It will blow out under normal pressure. The seal at the top is not that great and will not hold under a high load. If the pressure is high enough it can also come out of the the other seals in the engine too. Since he said the engine is clean, I would guess that it was the sender. If you don't have anything usful to say shut the F-up. :flipoff2: .

UMMMM Pressurized?? Why don't you get your manual out and read what the PVC valve does. Now if you have bad piston rings then yes your PVC valve or crankcase evacuation system may not be able to keep up with the blow by and then you will have a pressurized crank case. I know what Im talking about here. :mad: :flipoff2: :mad:

The oil level is perfect. ;) First thing that was checked.

Every Jeep 4.0 and 2.5 I driven or riden in ran at 210 degrees all the time, if the cold t-stat was swapped in, then as said above, rich condition, put your hand over the exhaust, does your hand now smell like gas, or does it still smell like ass? The oil thing is kinda freaky, but the sender would be my first guess, nothing like a mechanical guage to make you feel better about a new vehicle purchase.

By the way, the only crankcase I've seen significantly pressurised was in a 429 bib block Ford with some colapsed rings and valve springs from too much giggle gas, it was blowing so much oil out the breather that we unhooked the PCV and ran it into an empty 2-liter bottle so we could dump the oil back in every ten minutes or so, start knockin=time for a refill, and it still spanked half the trucks on the dunes. The video is hilarious, big lineup of quads, buggies, trucks, and my buddies Bronco with a big cloud behind it, the flag drops, and there's the Bronco out front with all the others choking on the smoke. I'm no Ford fan, but that thing gets it.

OMG! DEJeeper, WTF is wrong with you? You need to listen to Newbie Doc.......

you need to replace the oil over-pressurizer reader unit. it's located just above the oil pump but below the cam and right next to the # 6 cylinder piston return spring ;) :flipoff2:

I have edited the previous posts and conceed to Doc. Who knows were my head was yesterday. :emb2:

T-stat fixed the temp problem. This weekend gonna check out all these oil options ;)

bringing back this thread from the dead, basically same problem.
My temp reads a little low, when warm, not low enough to bother me just made me take notice. I had it sitting for about 2 weeks, and when I ran it today my oil pressure was damn near topping out the gauge at 80 with only about 2500 rpm. at idle it would be at about 50...previously it would stay at about 30 at idle and 60 WOT.

I checked oil, relatively clean but over due for an oil change by about 6 weeks...milage is only about 2k since last oil change, total motor milage is 83k, nad this is on a 99 XJ.

I also noticed my belts have some cracks...nothing really bad, all on the V side but lots of small cracks...assuming I should just replace that.

so wtf is up with my oil pressure??