260k miles and counting, i use castrol 20/50 year round

as for your missiing oil, the only weakness in a 4.0 is the rear main seal. if that is leaking itll be near the transmission housing. also make sure you have a good vacume seal on the line running to your valve cover. the one closest to the radiator. if that gets messed up you will leak oil from just about everywhere eventually

 

Damn, that's some thick oil for the 4.0...

 

This is a great forum. Thanks to all for the advice; shame we could not talk about this over a beer somewhere....

 

Hah! Dude, no kidding!

 

Well I thought the same thing, but has 260K on it?!

Tough oil pump for sure.

 

indeed, at idle it holds about 30 pounds, on the road it goes up to between 45-55 pounds. i started running 20/50 in every thing i owned in the early 90s. the old jeep also has been treated with slick 50 2 times, over its life.

sorry if ive thread jacked..wasnt intentional

 

There is one thing to remember. Oil pressure is resistance to flow.

If you have a lot of volume/movement, but the idle and running pressure is lower, that means you are getting a better flow and cooler oil to the bearings, etc.

Hot idle PSI should be around 13, while you only need 10 PSI for every 1,000 RPMs.

I used to think that high oil pressure was good, but not any more. It's kind of like high blood pressure.

 

Damn, that old engine is working pretty hard.

 

depending on youre oil change intervals i wouldnt worry about a quart. any more than that and i would start investigating... but you can check for leaks anyways, probably find some oil on the bottom of the oil pan, around the rear main seal and around the oil filter adapter.

mine has very slight leaks at the front crank seal, rear main seal, and oil filter adapter. leaks about a 1/4 quart every 5k