Low Oil Pressure Guesses

Sounds like worn bearings. You might try 15w40 (not 10w40) as this can boost pressure in a worn engine. Sometimes a can of STP or motor honey can help here too but a real fix would be new bearings and you should be able to replace them in car easier than a engine change. The 2.5 is a sturdy mill and not trouble prone in this area. You did not mention if you bought it new or the mileage on it. Also that engine tends to work pretty hard at times and 3K miles is a better change interval for it. I have one in my wifes 2000 Cherokee 5sp (we had a very hard time finding one with a 2.5 too) and it has been trouble free since we bought it new and it has over 80K on it now. Never regreted getting it with 2.5 either as it is mostly a commuter and it gets around 20 or so in town consistantly and around 23 to 25 MPG on the road with A/C on longer runs to kids college. It has gotten as high as 27. Motor has good torque for its size.

----------------- TheSnoMan.com

Dunno about your 2.5, but on the 4.0, there's a press-fit tube that has to be changed with the oil pump to get a good fit. Was that part of your pump changeout?

You did not mention

Um, I did buy it new, and I did mention that the mileage was 77,000.

Spdloader

Yep, the new pump came with the tube pressed in and welded.

Spdloader

I guess I missed that. Still it is unusual because that 4 is based off of old 232/258 block and is a sturdy design.

----------------- TheSnoMan.com

Another thing that you could do that is a bit extreme but would help even a new engine is add a external engine oil cooler as it cools oil before it reaches bearing which boost pressure in a hot motor but

----------------- TheSnoMan.com

Mine's got 90,000+ miles, and it still gets the same oil pressure as it did when new. The symptoms point to bearings.

Cheers,

Earle

I'm in denial right now Earle, humor me a bit.

lol

Spdloader

Even though you only have eighty thousand on, they may have been driven with the petal to the metal, just trying to keep up with the traffic, so your engine looks more like it just completed the Indy five hundred, switch to a 20/50 to squeeze another hundred out of it. Also with the blow by caused by the foot to the wood, contaminates would quickly clog the oil filter, and limit the oil feeding your engine and getting to the pressure gauge, so start changing her by a couple thousand. God Bless America, Bill O|||||||O mailto: snipped-for-privacy@aol.com

Pedal.

I think that the bearings are "select fit" on this model. You can't just order stock or 0.001" under and call it good. You have to plastigage every one and select fit the right size to each journal. The journals are probably scratched too. What did you do to it, so I don't make the same mistake? Good enough?

Cheers,

Earle

Just a thought, but could the overpressure bypass spring be b0rked and sticking only when cold just to open up when warm?

Does it ever return to normal? The early TJs have always had an instrument panel problem that sometimes gives erratic oil pressure readings. Sometimes mine goes down to nearly zero but eventually it returns to normal.

If it is select to fit it is because of production tolerances because it uses basically same bearings as old six it was based off of. I once tore into the crankcase of a 78 cherokee with a 258 that had oil pressure problems but it was not knocking, I found that the bearing that control end play was installed in wrong place and crank was flopping back and forth a bit. I do not knoe if it was original or someone had monkeyed with it but it had been that way for quite a while for sure.

----------------- TheSnoMan.com

Don't know for sure what happened. My wife drives it to work everyday, 7-8 miles one way. (to save the miles on her Eddie Bauer Explorer) She told me a couple of months ago she was seeing the "check gauges" light up, at idle sometimes, but I couldn't get it to do it when I'd go down and drive it. (The weather was still cold too) I did notice it was very, very low on anti-freeze when I serviced it for the spring, so it may have been running hot, I really don't think she'd know if it did. At any rate, since the warm weather is here to stay the "check gauges" thing has become consistent. One other thing, it rattles upon start up, lower end rattles, for about 2-3 seconds. Besides the other things I've done to it, I'm also running straight 40wt oil. Spdloader

Umm, huh?

Spdloader

No. It is consistent, and I verified it with a live gauge. Spdloader

The pressure gauge sender on the 6-cyls are notorious for going bad, have you confirmed your gauge reading with a mechanical gauge?

Somewhere back in foggy memory I remember an engine that had a ball and spring that kept the oil pressure regulated and one that bypassed the filter should it get cloged. But these days the bypass is built inside the filter.

Might have been a Triumph?