Oil Pressure Up/Down Light On/Off?

A friend has an 00 Cherokee and hes asked me to buy it. Issue is as decribed in the title and heres what he tells me...

"it started with oil light coming on, rev it a little and it goes off. last week drive it to work and oil light comes on and stays on. stopped, checked the oil, added a qt and light goes off. headed back home from work that day and light comes on and lifters are making some noise. limped it home, changed oil the next day, holds pressure for a min then looses it and light comes on and lifters rattle. light goes off and lifters stop rattling."

Has anyone had this issue? Sending unit or something else? He's priced it to me cheap but if I can still save this motor which I believe I still can at this point I would like to. The jeep has 210K on it.

put a mechanical gauge on it and answer your own question.

What kind of oil filter does it have in it? Is it orange??

Check the pressure with a gauge as said ^^^^. Then put a good filter on it. NAPA Gold, Bosch etc. Not an Orange one...then check the pressure again. If it's not the filter or the oil in it, worst case is a new pump IMHO

Sounds like the friend ruined the engine.

If adding a quart of oil stopped a lifter rattle, it was way more then a quart low. M uneducated guess is the engine leaks and /or burns oil. it's been allowed to run out of oil on multiple occasions and the main bearings are fried.

Excessive clearance at the main and rod bearings(from wear) allows too much oil out of the system too fast. The oil pump can't keep up at low engine speed, so the oil pressure drops. At idle the pressure drops so much that the light comes on. with low enough oil pressure, the lifters collapse. Pressurized oil keeps hydraulic lifters "pumped up". With insufficient oil pressure, the lifters bleed down, and you start hearing the rattle from a loose valve train.

When the engine is cold, the problem either gets better or goes away entirely because the cold oil is harder to push through the gaps and the pressure stays higher at lower RPM. Once the engine warms up, the problem reappears or gets worse.

Sometimes you can "fix" an engine like this with 20-50wt oil. The thicker oil acts like the regular oil when it's cold. This won't last long though. Eventually(sooner rather then later) somebody's going to have to break down and rebuild the engine, or it's wrecking yard time.

If it's really cheep, and the body is in good shape, it would be a good project. If you're buying it intending to drive it right away, plan on a new engine immediately and price accordingly. If you want to do the swap yourself, any '00-01 XJ or '00-'06 TJ motor will swap in. Conventional wisdom is stay away from the '00 model years because of a head issue(search for "cracked 0331 head") but the problem is somewhat overblown.

My co-worker recently ran her '01 low on oil and the valve-train sounds worse than a diesel engine and might even have a collapsed lifter in cylinder 6(P0306 misfire, and I changed the plugs). The TUPY head was installed by the used car dealer she bought it from, so no, the 0331 head issue is not overblown(she didn't heed my advice on staying away from 00&01s and payed 2Xs more than what I could've found from an owner).