IGeeky1

Assume: 93k miles, the 0331 cylinder head is cracked and oil pressure is only 20psi hot at 2000rpm and drops to 4 at 700 rpm.

Oil was changed less than 200 miles ago. Currently have carquest blue oversize filter and rotella T6 5W30

Are bearings guaranteed shot? Or is there a possibility replacing the head and flushing oil and coolant will make the jeep and me happy again?

OK which bearing are most likely bad? Seems the ones with the most coolant contact would be the ones replaceable by pulling the oil pan.

jebmccall

have you verified the low oil pressure with a mechanical gauge??? do you have internal coolant loss?

these are two of the key factors in deciding where to go.

just for reference oil pressure spec is minimum 13psi att hot idle, 37 plus above 1600 rpms when hot.

if indeed it does have low oil pressure due to coolant in the oil and you have caught it early enough it does not mean the bearings are trashed neccesarily. v erify the two above questions first though please.

1976Mustang

Do you -KNOW- the head is crack or assuming? It could just be a gasket. Bearings should be fine if it's been getting some oil, the bigger issue would be increased engine wear.

Turbo X_J

Since it's your money I guess we can assume anything thing you want. If it was my money I want hard evidence of a problem before I'm laying out in driveway in 2 feet of slushy snow swapping motors.

How long has the oil pressure been so low, and why the sudden concern now?

DFlintstone

Cracked? Are you loosing coolant? Was the old oil milky? (or creamy stuff in there)

The oil pump circulates the oil all over, cam bearings ect.

IGeeky1

The 2001 Cherokee has only been mine for a week. I've only put a few hundred miles on it. Change oil and filter. The stuff I took out was ugly black but not milky. Filter also seemed very full. I really haven't driven it enough to know if I'm losing much coolant, I need to do a flush, put in new coolant and give myself a baseline I guess.

Also looked to have a leak in valve cover gasket and perhaps rear seal, things were pretty gunky. Again I cleaned things up a bit but have not driven enough at this point to pinpoint. Rather figured if I needed to replace head that I was then gonna drop oil pan as well and would replace seal then as a matter of course.

I recently checked compression and it was good in cylinders. Then replaced plugs. I now have the valve cover off and things look really crusty. Will be running it tonight with cover off to see oil flow and see when hot if a visible crack show its ugly head somewhere between cylinders 3 and 4.

This thread with its assumptions was just that...with oil pressure behaving how it is, good cold and bad hot, what other scenarios are there other than crack in head? AND if head IS cracked does the poor oil pressure indicate bad bearings? Just the mains or..?

I guess this is all due to me not understanding how oil pressure is related to the bearings. Is oil pressured into bearings or are the bearings just soaked in oil? I though just soaked so have a hard time understanding how their being bad could relate to oil pressure.

Bustedback

Low oil pressure is caused by excessive clearance in the main, rod, and cam bearings. You may not have a rear main leak, it could be the oil filter adapter o ring leaking and blowing back. The crappy looking coolant could be a good sign of there not being an issue of losing coolant. You could assume if there was a problem with losing coolant it would look new. Just keep an eye on it.
The bearings are not ball or roller bearings, they are friction bearings. They are made of soft material that will trap harmful debris to keep from damaging the journals. There is only a thin film of oil between the bearing and journal, the spec is .0015-.003" of clearance, any more than that will cause low oil pressure. The oil is pumped through passages in the block, crank, lifters, push rods, and to the cam bearings. Oil leaks will not cause low oil pressure, just a mess.

RTorrez1

^^ This is the first thing you should do before assuming the worse.^^

jebmccall

ok... going on the assumption that the jeep is using coolant, and the oil pressure gauge in the dash is correct i would assume the bearings are trashed most likely due to a cracked head which the 00-01s are notorious for... but thats just an assumption, more than likely at that milage its just a bad sending unit. i would check it with a manual gauge, if it shows a different reading at hot idle then i would put a new mopar sending unit in. drive it and see if its using coolant.

DFlintstone

The oil pump draws oil from the pan and pressurizes little passages in the engine that feed things like the bearings and lifters. If they are tight and new, minimal oil goes through and pressure stays high. (there is a regulator with a spring to keep it from going WAY high and wearing out your pump, it just lets extra oil go back into the pan).
When an engine get's old and "clearanced" (worn), more oil gets past the bearings and the pressure drops.
Double checking the dash gauge might well be your first step. It has a sending unit that might not be good, as well as the gauge its self. I'm not sure, maybe that is something you can rent? (a mechinical gauge, to be screwed in where the sender goes by the oil filter)
No, highly doubtful an 1331 crack its self will cause low oil pressure. Coolant or water in the oil from a crack can though. Maybe all that "went down" and the PO, flushed it, then sold it? Water/coolant in the oil will turn it milky and make sort "yogurt" like stuff, maybe on the dipstick and under the oil cap. OH! And, I've seen posted that the passage behind the sensor can get clogged up. Probably something to check. (I might just crank it a sec with it out, see that it squirts).

Radi

Got any engine noise to go along with that low pressure reading?

IGeeky1

Yes there is a noise when it runs. I'm pretty sure I identified the cause of the noise. The 5th rocker in from the firewall (so on cylinder 4) is loose, as in I can wiggle it and make noise by hand, can't do this on any others, bolt on top seems tight.

As per crack...couldn't see one. Picks here. I've read the crack is usually between cylinders 3 and 4 on the 4 side, so that is where I cleaned and shot. I took engine up to temp with valve cover just sitting on and me pressing down just a tad on it. Once oil pressure dropped I shut off engine, removed valve cover, cleaned and shot.
https://www.dropbox.com/sc/uplopvpoc8kbttp/kqVaZJ6kJ8

My next step is to figure out how to alleviate the loose rocker on cylinder 4.

I keep meaning to pick up a mechanical gauge to test oil pressure with...grrr

Then, I plan to clean up a bit and install valve cover with rtv only on head side of gasket so that if I need to I could remove valve cover again. Coolant needs a flush anyway so I 've been told filling with non-glycol may help things last a bit longer if there is a crack so I may as well refill with that and then monitor.

Then it off to the bottom side to see if the only leak was from valve cover gasket or if there are more and I then may need to pull oil pan. I know nothing of how to remedy my rocker know so once I investigate that it may require me to pull oil pan any how...we'll see.

Thoughts and suggestions always welcome! Thanks for all the time and responses everybody!

IGeeky1

So I see you don't adjust rockers on the 4.0 Also saw that checking them static doesn't matter but the intake on cylinder 4 is always loose no matter where the engine stops and the rest are all snug

videos https://www.dropbox.com/sc/qcsl6ae7n63by7v/vAinhoqJbq

So this means lifter is bad?

bigbadon

It takes awhile for them to bleed down. #4 lifter appears that it is not pumping up. Other possibilities could be worn cam lobe or worn rocker pivot. You seem to be getting plenty of oil to the rockers.

DFlintstone

At least plugged, not pumping up, oil pressure?. Pushrod spin true? (if you spin it does it wobble? Same as the others? Does the valve seem to be the same height as the others? (not stuck down).