00exjay

2000 Cherokee just replaced cracked head with a non cracked head. Oil pressure is 40 at cold idle and 5 at hot idle. Confirmed with mechanical gauge. Used motor flush to clean sludge used thicker oil and Lucas oil and still 5 psi at up idle. Swapped oil pump for high volume pump and new pickup tune. Is there anything else I can try before I have to bite the bullet and go for a rebuild?

00exjay

Also the motor makes a little noise and I believe it's the rocker arms. It's not knocking.

Radi

For the heck of it, did you try cleaning out the oil port the pressure sender attaches to?
I assume you connected the mech. gauge to the same port?

00exjay

Yes and yes I ran the motor for a minute with the sender out and oil squirted out. This guy who owns a shop said something about oil pump bleeder spring? Know anything about that?

00exjay

Also I saw something about shimming an oil pump for more pressure what does this mean?

Radi

You already replaced the oil pump it appears. The problem is most likely elsewhere- like engine bearings. This happens somewhat frequently with cracked heads, coolant mixes with the engine oil and destroys the bearings.

00exjay

But if I had worn bearings would my oil pressure be low all the time? I got 40-45 psi at cold idle and the pressure goes up with engine Rpms

jpowersxj

low oil pressure and a knocking. check the arms and make sure the rocker arms are the right torque. if it were the bearings you would probably panic from the loud rattling and shut her off half *****ing your pants. is it a digital oil pressure sensor i would replace the unit if the engine seems to be running fine. otherwise check for a leak near near the crank.

bigbadon

If it makes you feel better I had the same problem (4 at hot idle and 20 at 2k) and I have been driving all over the state for a year...saving for a new engine and still waiting on the catastrophic. This has turned into a quest to see so how long it will last. No need to use Lucas it won't help. Increasing oil pressure will not make up for a worn engine. If yours is not knocking you probably have some life left so don't panic.

Kalali

The high(er) oil pressure when cold is normal since the oil is thicker and the pressure drops as the oil is warmed up and thins out. I think what you are experiencing is damage to the bearings due to prolonged use with a cracked head. There are a lot of folks here who will tell you that they have driven thousands of miles with (hot) oil pressure in the 5-10 psi range with no issues. If you have no audible symptoms (aside from a little ticking, etc.), I'd say just drive it. I would make sure the rocker arms are installed and torqued properly if you hear a tapping (vs. ticking) noise.

97AT4x4XJ

Running motor w/o sender means your bearings didn't have any oil.
I wouldn't run my engine w/o sender for more that 3 sec.

00exjay

Rockers are torqued right we did the head about a month ago and I guess I'm just gonna drive it. Just wondering if there is anything else to do before a rebuild

97AT4x4XJ

Oil pressure at 1600 RPM and higher should be 37-75 PSI
Is it?
Is idle speed OK? Too low?
Check idle speed.

00exjay

Tac shows at about 500 rpm

Gorillaxj

I agree with the above.

What I did with my 2000 after doing the things you have done, was run 15-40W oil, as its thicker hot and cold and will not bleed off threw the worn bearings as much as the 5-30/10-30 most people run. giving you better pressure at idle (only buying you time) as the rebuild is inevitable. Mine had worn mains/rods and oval-ed cam bearings when I tore it down for a rebuild. The cam actually had slop and was not turning straight in the bearings... but it never had a knock or any symptoms other then lack of pressure hot at idle.

I built a stroker with a high volume oil pump, I now have 80psi cold, and 40psi hot.