I recently bought this 2001 jeep xj 4.0L sport in kinda rough condition, it was supposedly in a flood but no wire damage whatsoever. I get low oil pressure at idle (8psi) and it goes up when on the gas. its at 35psi cruising on highway, 25 around town.

I never let it go above 2000rpm without revving it up to get the oil pressure up (at least 20psi). check gauges light comes on when it's at 8psi but the gauge says zero. I'm using 20w50 oil currently

The mechanic says my cam bearings are shot and it would be a lot to fix so I'm just going to get a new engine.

Main question is, how long would this current engine with 119k on it last before it finally kicks?

(replaced the oil pump and sending unit already)

 

Does it exhibit unexplained coolant loss?

 

No coolant loss, I've already checked and assured that it is not a cracked head.

 

4.0 will survive with that5 kind of oil preessure, however that 20w50 will kill it, to thick to provide enough flow. youre bearings are starving....

im guessing you have verified youre oil pressure with a mechanical gauge???

what filter are you running??

for oil the 4.0 likes 10w-30

 

i ran my 99 cherokee with severly low oil pressure for 45k till i wrecked the thing... it knocked a bit but it kept going. at 2000rpms it had 15psi, at idle it had 4psi.

 

If it ain't knocking relax and drive it. Get rid of the 20-50 in favor of Rotella 15-40 or Wally supertech 15-40 diesel oil. 2000 & 2001 4.0s have a history of low pressure,sometimes it is due to the cracked head issue but not always. There are countless stories of people rebuilding their low end and still ending up with the same pressures.
Mine has had 4psi at 650 and 20 psi while driving for a long time. If your rockers are getting oil to them everything else will be too,the law of gravity will flow oil down to the crank. While not the ideal situation your engine will survive from low pressure....it is what is CAUSING the low pressure that will eventually destroy an engine, not the other way around. The 216 and 235 cubic inch chevy and GMC six cylinder engines did not even have a pressurized lube system,instead they depended on oil just splashing around. They were some of the toughest engines ever built.

 

The first thing you should do if you are concerned about the oil pressure is to verify it with a mechanical pressure gauge. You can rent one at any auto parts store such as Auto Zone. Also what brand of oil filter do you have on it right now? If you have a Fram filter on it get rid of it as soon as possible and install a quality brand filter such as Mopar, Wix or Napa Gold. The Fram oil filters are CRAP and can cause low pressure and dry starts.

 

It doesn't make any knocking or any other noises.

And for the oil filter I have not a clue what kind it is, it's blue if that helps lol. I'll check tomorrow if i remember.

I'm going to run this oil until the weather warms up at least because it's only been in there for about 500 miles and it seems to run better than before.

I bought it from a kid who had no idea what kind of jeep this even was so it was impossible to find out any kind of information regarding the previous oil used.
All he knew was it was a flood salvage and that the color was black...

 

run it if you want but 20w-50 is no good for a 4.0 especially in cold weather.
when you go to an oil change get a wix or mopar filter, along with some decent 10w30. my preference is shell rotella synthetic blend 10w-30.

i know you said that you want to run the 20w-50 till it warms up but in cold weather it is even worse due to how thick it is. a 50 weight oil is only suitable for race applications where the oil gets really hot and thins out to what is desired.....

lower oil pressure on a 4.0 is ok..... to an extent. as long as it doesnt make any noises you can run with it, one thing you can try doing is removing the sending unit, get a 5 gallon bucket run a hose from where the sending unit would go into the bucket. run the jeep for a 5 seconds and then shut it off. check to see if any crud came out. if so that is not uncommon in 4.0s that have been neglected. that crud will distort the reading of the sensor.

when you had the oil pump replaced did you inspect the rod or main bearings???

 

What he said and use OEM spec oil weight, 10w30, and lighter oils like 5w20 will be fine for cold weather. NEVER run a heavier oil than the factory recommends, it won't get into the places it needs to go and makes it harder for the engine to run. The AMC242 (4.0) will go forever if you maintain it properly. There's some guys here with over 400k miles on their engines with no issues. I'm personally at 221k miles and it;s never had an issue.

 

If you live in the salt belt, it'll outlive the frame and body.

Pay attention to the comments about flushing the pressure sender port, checking with a mech. gauge for a baseline, and running a more temperature-appropriate weight. 20/50 is just too stiff, particularly in the cold. I run 15/40 in the summer and 5/30 in the winter. 240,000 miles and no issues.

 

Honestly, you need to read the motor oil 101. That 20w-50 is way too thick at start-up, especially on cold days, and I imagine it is too thick at operating temp as well. Leaving that oil in until it warms up outside makes no sense really; if anything you should be running a thinner oil in cold weather, not thicker.

 

I'm lucky, I can run 5w30 all year in so cal

 

hard to say. if you're easy on it it could last a while. Oil pumps are fairly easy to do, you could opt for the high flow version and prolly make it last a bit longer

 

Change the oil!