sheepdog

today my dad and i went to look at a jeep for him, a stock 1997 4 liter country, auto, w/135,000 miles, everything looks great about the jeep, just a minor oil leak, no drips or anything, body is 90% clean, interior is very nice. BUT, when we started it, 25 psi on the oil pressure. we took off, and the highest it ever got was around 35 registered psi, then got off the highway, turned around to head back, and while going 65 on the highway, we were reading 10 psi!!!!! we came to an idle at the stoplight, and we couldnt hear any knocking or any other engine noises, and the jeep had better acceleration than my jeep with under 100,000 miles, granted mine has 3:07 gears and 31 inch tires.....

but it had good power, drove smooth, no bad oil leaks, but never got above 35 psi, and got as low as 10 psi, and we never heard any engine sounds. what could be causing this? is it still worth paying $3,000 for?

wildbill1

If the oil pressure readings were accurate and you only had 10# at highway speed, I'd be hesitant to buy it unless you plan to do some work to it soon. As far as 25# on start up at idle, that's fine. The only way to find out for sure is to install a mechanical gauge and see if the factory gauge is giving accurate readings. Sometimes the sending units get flaky and give false readings.

89Renix

i dont know if it helps, but my buddies ZJ had the same issue, his would drop down to 5-10ish, turns out.

A. he was low on oil..
B. he was running too thin of oil

rand4x4

My oil pressure sending unit was gone when i bought mine, If it looks like it is leaking around it that is most likley it. It is just above oil filter.

Bstrom650

Does that mean that a high oil pressure reading indicates 'too high' an oil weight? I'm getting 70psi gauge readings and use a 10W-30 synthetic oil. Backs down to around 60psi after it warms uyp and been on the road a bit but when cold it's 70psi each time. I'm a new owner o a '96 with 187,000 miles! Runs great, plenty of pep, no leaks or burning.I just don't get it... might it be the sending unit?

mentalbreakdown00

BStrom no you are fine, mine does it with any 30 wt, I actually run 0W30 and it'll still hit 55-60 psi every morning at startup.

On to the Original Post, you may have an actual mechanical problem, or you may just need an oil change badly, or may be a sending unit. I would check it or negotiate them down because it may need major work.

tjwalker

Verify, verify, verify!

1. Get a mechanical gauge (they can be rented from some big box parts stores)

2. Temporarily install it where the current oil pressure sending unit resides, which is right above the oil filter. This is a 10 minute swap.

3. Compare the readings of the known good mechanical gauge with the dash gauge.

KNOWLEDGE IS POWER. You must know what is going on before you tender an offer.

The spec for the 4.0 is as follows:

*Not less than 13 psi at HOT idle
*Between 37-75 psi over 1600 rpms

Good luck and let us know what you find!

vistacruiser

I've got about 270K on my 98 XJ. I believe I'm on my third or fourth oil pressure sender ..... lost count ... if that says anything.

sheepdog

ya i asked the guy to replace the sensor, and let us know if it fixes it, as i had to replace mine when all of a sudden my oil pressure was reading 120 psi, and when i let off, 0 psi.....but at that low of psi, wouldn't you be hearing the engine ticking or making some kind of unwanted noise? it the sensor doesn't fix it, it could be the sending unit.....

tjwalker

The sensor and the sending unit are the same thing.

No, you wouldn't hear anything with 10 psi of pressure.

Again, must be verified. You need to know.

sheepdog

oh. haha. i feel dumb lol i was thinking the oil sump, like whats in the oil pan. but i guess that would possibly be more obvious...
ya my dad got a mechanical guage, he borrowed it from the local tire/tow/salvage/windshield shop. my dad is a highway patrolman, and since he works ALOT with the tow truck drivers, he is good friends with them, so they are letting him borrow it.
'on a different note, do you think a 97 country w/135,500 miles, clean body with good paint accept a small dent on the front right bumper cap, auto tranny, d-35 rear is a good deal for $3,000?

sigsandjeeps

No...it seems a bit high, but it might be the area. I got my 97 with 160 on the clock and minor body damage for 1200. Oil pressure does the same thing. Every time I hit a bump it fluctuates. It's been said on this thread. Check it with a mechanical gauge.
Good luck and hope you can figure it out.
sigsandjeeps

tjwalker

A perfect 97 "might" be worth 3k. Otherwise, a little high. And a LOT high if there is any kind of doubt about oil pressure.

Get the results of that oil pressure test.

If hot idle is below 13 psi, either pass on it or bid a price that allows you enough money left over to (worst case) replace the engine. That would be worst case, but you should ALWAYS figure "worst case" in situations like this. Take it from somebody who eventually learned from his mistakes!!

There were a lot of XJs made. Take your time. Be sure to look at as many rigs as you can.

RTorrez1

I agree. $3000 is a bit high. I pick up my 98 XJ with only 89,000 miles for $2000 and it was in great condition it even had a killer stereo system. i would differently check out the oil pressure problem before making an offer.
Good Luck

sheepdog

we checked it with a mechanical guage, and the oil pressure is good. read like 40 at idle, and when the engine was up it read around 60ish. we have looked on ksl for jeeps for about 6 months, and this is one of the best deals we have found. i have also been shopping other places, and just cant find anything for cheaper....i dont know. maybe the area. meh. my dad got it, it is in really nice shape, but it does need u joints, they are a bit wobbley when i got down and checked...has good alpine speakers and a pioneer premier head unit, and wired for a system, so i put in my kicker 12" and an mtx amp for my dad. sounds pretty good. not as good as my infinity 12 and kicker amp though.....it does have the up country package though, and 3:55 gears, which is good, he doesnt plan on putting any bigger than 30" tires on it.