• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Low oil pressure at idle when hot

stephenspann27 said:
Bummer that you are having those problems with such a "new" XJ. I wouldn't order anything until you've checked the oil pressure with a mech. gauge. A compression test may also review a head gasket leak/cracked head.
Click to expand...

I did check the pressure with a mech. gauge, it matched the electronic one exactly.
 
Kevinma255 said:
When you replaced the rear main you had to pull the rear cap. did the bearing look ok. I agree that that is the most probable place to loose oil presure but what about the port by the distributor. is it possable that it is worn at that bearing. I am thinking old chevy/ford motors so I am not sure the 4.0 is the same. If it was running at 0psi for any amount of time I would think the crank and cam would be hurt, not just the bearings.
Click to expand...

When I pulled the rear cap the bearing was smooth to the touch and quite shiny. All the images I had seen before of bearings that were shot did not look like that. Also the 2000 model year 4.0 does not have a distributor, it has a coil pack rail, so I'm not sure where you would be referencing.
 
winterbeater said:
Just doing the rod bearings probably won't get it most of the time. The crank mains can also be done in the vehicle without pulling the crank. The problem is the cam bearings which will also bleed off oil pressure.
Click to expand...


The cam do in fact have a direct high pressure feed from the oil pump. The hydralic lifters need plenty of oil to keep them full at all times.

All the mains and connecting rod bearings could be done without removing the engine. The cam bearings however is a different animal. Maybe they could be done if the radiator is removed?... then again not. The rear-most bearingis backed by a disk similar to a water jacket disk that have to be pushed out in order to get the bearing out;... or is this only on V8's? I have yet to rebuild a 4.0L.

Anyway, I would look at all the easier things first before I do bearings.
 
You already replaced the oil pump (which was a long shot anyway). The only thing left is to rebuild with new bearings. Thick oil is a stopgap measure which will actually wear out other parts more on cold start up. Hey, best plan is to get another motor and take your time rebuilding it right while you keep wheeling on 50W. Or start to look for a low mile motor on craigslist. If you need one quick, you won't be able to find a great deal, but if you start looking now, who knows?
 
About the cam bearings and oil pressure, when I had cam bearings put in my LT-1 block, the engine build put the last bearing it so that only half of the oil passage was exposed in order to bump up the oil pressure. Doing the main bearings from underneath looks like it would be a pain..
 
Ok, does anyone have any opinions about the best place to buy a rebuilt head and/or engine? I'd probably feel comfortable doing an entire head and/or engine swap, not so much confidence in trying to do a complete rebuild myself. That and from the browsing I've done a 2000 or newer engine with the electronic ignition seems a little hard to find.
 
bdbell said:
Ok, does anyone have any opinions about the best place to buy a rebuilt head and/or engine? I'd probably feel comfortable doing an entire head and/or engine swap, not so much confidence in trying to do a complete rebuild myself. That and from the browsing I've done a 2000 or newer engine with the electronic ignition seems a little hard to find.
Click to expand...

Search the 0331 head threads and you'll find a lot of info on that stuff.
 
I finally checked the torque on my connecting rod bolts and found they were tight, but i had some play in them. Looks like that is my engine problem. Time to start saving up for a new one. I not enough of a motorhead to stroke it or replace the stuff.
 
time for a stroker dude....
 
I got a motor from a guy on Craigs list for $350.00 complete. if you look you can find them. good luck. btw if you have the book with torq specs and know of a ok machine shop to check the walls and seat the new bearings a rebuild is not that difficult, good luck
 
So for further reference for people who might google this later, here is what I think has happened. I cannot confirm any of it yet, but it's an educated theory:: About 18-24 months ago I blew the upper radiator hose. Replaced. About 4-6 months later I blew the lower radiator hose. Replaced. Had lots of trouble getting all the air out of the system. (There is a service notice on this problem. It's a PITA.) Failed to notice that under pressure the block-side clamp of the lower radiator hose was leaking under pressure, ran low on coolant and engine overheated. Testament to the engine that it took that long, since I poured back in almost 1.5 gallons of coolant. Happened again a second time after I took it into to the shop to have it pressure tested. So, overheated twice. Combined with strong anecdotal evidence that the heads on the early 2000 models had a strong likelihood of cracking especially after overheating. I believe that after the overheating the head cracked slightly and started to leak coolant. This coolant got miniamlly into the oil and was being consumed in the cylinder. The consumption was being masked by small coolant leaks in various places (overflow tube, etc.) The assumed coolant in the oil began to eat the bearing surfaces and caused them to wear out, opening the tolerances and causing the drop in oil pressure when both the oil got to temp and the entire engine reached operating temperature. As soon as I save up enough money to do a rebuild / swap I will be able to confirm this story.
 
Update on mine

I finally got the new timing chain and High flow pump installed. So far my pressure has been excellent. Starts and runs at 60 psi and once it warms up and driving it is at 40 psi. So you can try that and get a lil life back into the motor.
 
XJ Stryker said:
Update on mine

I finally got the new timing chain and High flow pump installed. So far my pressure has been excellent. Starts and runs at 60 psi and once it warms up and driving it is at 40 psi. So you can try that and get a lil life back into the motor.
Click to expand...

Good news Stryker. Trying to add to my XJ knowledge as almost all I read hear said that a new oil pump usually never fixed anything. In an earlier post, you were also asking 8Mud about bearings. But what I see now, you ONLY replaced the oil pump and timing chain. Is it correct that you did not change bearings?
 
winterbeater said:
Good news Stryker. Trying to add to my XJ knowledge as almost all I read hear said that a new oil pump usually never fixed anything. In an earlier post, you were also asking 8Mud about bearings. But what I see now, you ONLY replaced the oil pump and timing chain. Is it correct that you did not change bearings?
Click to expand...

I thought about changing the bearings but then backed away from it. I only did the above and went from about 2psi at idle to 40 so it is a major improvement.
 
You must log in or register to reply here.

Similar threads

O
0331 Strikes Again...?
Replies
11
Views
325
Ol Blue
O
A
1987 4.0 oil pressure problem
Replies
1
Views
1K
RCP Phx
R
J
Running just fine then dies at idle on street
Replies
4
Views
2K
90xj06
9
J
AW4 Problem shifting first to second when hot
Replies
2
Views
1K
cruiser54
C
M
Oil pressure question
2
Replies
26
Views
3K
Money_Pit_Incoming
M
Back
Top