Hello, I'm new to the jeep thing. I have a 98 jeep cherokee with good oil pressure when it first starts up. It's at about 42psi, but once it warms up the pressure drops to about 10-12psi. Is this normal to have such low pressure? What should the psi be at? I use the recommended 10w30 when I do my oil changes and I'm worried my main and connecting rod bearings are worn out. It has a 6cyl 4.0 with 139000 miles. Could it be a bad oil pump? Any ideas would be helpfull. Thanks a bunch...

 

Well mine sits at around 60 cold and 40 to 45 when warm. Your pump may be going.

 

You need 10 lbs. of pressure for every 1000 RPM.

If you've got at least that, you're OK.

 

With the engine cold and then warm reve the engine a few times and see if you hear any unusal knocking which would indicate bearing wear. My Oil pressure was low so I installed a high volume pump and now its 50-60 PSI cold, 30-35 at idel, and 40-45 when driving. Most likely a bad pump is my guess but you can put a mechanics gauge from Harbor Freight (about 10 bucks) on where the existing sending unit is and get a more accurate reading. I've read that 9-13 psi at warm idel is normal but the as low as 7 PSI is good enough. You want to be around 35-45 while driving at normal temp if not higher.

 

Same deal I have as well when I drive normal operating temperature I am in between 40 and 50 PSI. I came to a red light and dropped all away to zero PSI . I turned her off for little and then had my lady turn her over while I looked through the oil fill hole and I could see that there was minimal oil lubricant at the top end. I drove my friends truck home and left it there. Didn't want to risk blowing a brand new IL6 4.7 stroker. (Lesson for future: don't cheap out when building a new engine.) oil pump is from the stock 4.0L .

 

Yup, that's the basic rule.

You might just have a gauge issue too. Get a mechanical gauge and check.

 

Minimum acceptable oil pressure is 13 PSI with the engine at hot idle. You may also want to validate your gauge with a mechanical gauge just to be sure. A Jeep 4.0L engine with (only) 139K miles is only half way through its useful life.

 

What's up fellas
I've been having this same issue but my 4.0 is hitting 175k but it's having this weird shimmy metal noise at around 2k rpms shifting through gears...
98 4.0 5speed....
If anyone has any inputs thanks in advance...

 

Bingo, that's always the 1st thing one should do when suspecting an oil pressure issue......a mechanical oil pressure test gauge. Don't have to buy one, borrow one if u can or have a shop test it.

 

What if the oil pressure gauge shows it maxed out. 99 XJ 4.0 runs fine with no odd noises. Currently at 209,500

 

Bad gauge. If was that high the pump drive would be wrung off

 

Check your rods, the bearings will look good if not knocking in most cases. They are out of rod. Some where around 92, they were made to be a weak link. Mine only had 113,000, but rear main seal was leaking. The bearings looked good. The oil pressure was good when I started cold or the first start and would drop to 5 psi. It would go up if I raised the Idle to normal psi. Then drop right back down if let off throttle.