low oil pressure... still
 

just bought my first xj with 180000 miles the po just re did the bottom end and camshaft bearings. he also replaced the stock oil pump and screen with a high volume oil pump. the jeep had low oil pressure on a hot idle so i put 20 50 in it and it was great at cold but when it warmed up it went to zero
i just put in the stock pump with 6 qts of 10 30 and a qt of lucas oil stabilizer and its running like when i had the 20 50 in it. i am thinking of putting in 20 50 again and see what happens what do you guys think?

I replaced the oil sensor next to the filter and it solved my issue. It was bad. Cost $30 for my year. Older years are $10.

i checked my oil pressure with the gauge and got a new sending unit and the gauge is like 5 psi more than the sending unit so its fairly close to actual

First thing you want to do is Verify that you really do have low pressure by installing a mechanical gauge. You can rent one from any auto parts store.

Read his post before yours...... He did that already.

i heard one guy on another forum said his was clogged so i took off the sending unitl and gave it hell for a minute and oil went every where plugged it back up and it still says zero. when i get off work in the morning im gonna put a pipe cleaner in it and clean it as well as i can than let some more oil squirt out and see what that does than if that dont work i guess ill do some 15 40 and see what happens

Sheez, so he did all that and still no pressure. I might double check in the dizy hole and decide if I think if it's really going around. Just pulling the sensor and cranking it seems a good way to see it that's clear.
I'm not familiar with the pressure relief valve on the 4.0.

Let's back up a bit. First of all, you should post the year/engine for every thread. I'm assuming this is an 01? What do you know about the history of this Jeep? Why did the PO do the repairs. Knowing this is critical to determining "root cause" here.

The 00-01 from the factory came with the infamous 0331 cylinder head, which has a bad habit of cracking between cylinders 3-4, where there is a known casting defect.

I think it is entire plausible that is what happened to your XJ and the PO tried to resolve it, but hasn't had the best of luck with it.

Here is a link to a thread that you may be interested in, but it's a long shot. My money is on internal bearing problems caused by a cracked cylinder head. The PO did not do a complete rebuild which is what you will likely need in the event that the head cracked. Hope I'm wrong, but I've seen enough low oil pressure symptoms on the 00-01 to know what to look to first. And that is a cracked head.

http://www.jeepforum.com/forum/f19/4...fixed-1304679/

iit is an 2000 and i looked at that thread and put a pipe cleaner as far into that hole as i could and cleaned it up than let it run for a second with the sending unit out to let the oil squirt out to clear it up. i just changed it to 15w40 and still no luck. its slightly higher. how could i tell if i have that cylinder head? or does every single 00-01 xj have one? also how could i tell if it were cracked water in my oil?

could it be the oil pump pick up tube? i didnt replace that cause when i dropped the pan it looked brand new still. it came off the high volume pump and slid into my stock pump just fine and fit like a glove

Unfortunately, (or fortunately), I haven't hands-on, been there with that. Don't know how the pickup tube seals. It's gotta be good of course. Any air sucking in, and the pump won't pump. Guess some design's DO use O rings (which age and harden), on a vacuum side..anyway, on my 90, the head cast # is pretty clear just past 1/2 way back, facing up, on the drivers side top edge of the head.

thats where it was it said 0331. so does my jeep having the 0331 head an automatic death sentance? like if i have this cylinder head it is automatically cracked?

CALM DOWN!
Maybe I I already read it and his last post wasn't up before I put in my post!

He posted it 31 min before you posted.... Your argument is invalid....
And I am calm.... Just letting you know.

easy does it were all on the same team here haha
so my jeep does have the 0331 cylinder head
now how do i know for sure that my head is cracked there dosent seem to be any coolant in the oil or vise versa. i think ill drive it a little more and see if any bubbles re visible
are there any other ways to see if its cracked without taking stuff apart?