After noticing low oil pressure at idle and at cruising speed in my 1990 XJ 4.0, I parked it until I could do a little diagnostic work. I pulled the oil fill plug and observed the engine running, hoping to see some oil splashing around, which I saw little or none. Plan B, changed out the oil pressure sending unit, which made no difference in the oil pressure reading. ( ranging from zero to less than 10 psi) Plan C, hooked up a mechanical gauge and confirmed the same pressures as the stock gauge. Now I'm thinking oil pump replacement. I bought this XJ about a month ago, and the odometer shows 213,000 miles. The seller said that the motor had about 100,000 on it. It does not smoke or have any valve noise, so I'm hoping that replacing the oil pump will extend the life of the motor without replacing it right away. Anyone else have a similar experience?? Thanks in advance for your input.

Mark Inskeep
1990 XJ Laredo

 

oil pump does not make pressure bearing clearences dohttps://www.cherokeeforum.com/f51/ho...e-works-82130/

 

Check this out:

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

 

Interesting link. Easy enough to try & cost nothing but a little time. Thanks will use this in future if ever needed.

 

Thanks for the link. I'll check it out and report back.

 

I know that it's been a while since the original post, but I was kind of busy with work and things. I've had a chance to dig into my low oil pressure issue a bit deeper. Last weekend I drained the oil, which looked decent and dropped the oil pan for a good look at whats going on in there. My engine has over 200,000 miles on it, and it was surprisingly sludge free inside. The screen on the oil pick up was even clean. I pulled a main bearing cap off for inspection and the bearing surface looked good, no brass showing or obvious signs of damage. I decided to go ahead and replace the oil pump and see if that was my problem. I ordered a stock Mellings oil pump, a Felpro pan gasket and a Wix oil filter from Summit Racing. My parts arrived this past Wednesday, and I replaced the pump and buttoned her back up this afternoon. After filling up the crankcase with straight 30w oil, I hit the ignition, and the oil gauge instantly showed 60 psi at cold idle. I took a test drive and the pressure stayed above 40 psi and about 25psi at idle. I'm going to keep a close eye on things and see how it goes. Hopefully, I can get a few more miles out of her before I have to go engine shopping. Thanks to everyone who commented on this thread, I really appreciate your input.

Mark Inskeep
1990 Laredo

 

would not suggest running straight 30 weight oil. to thin to protect. go 5w30 or 10w30. high mileage. blended oil. or rotella.


high pressure dosnt always mean higher protection. trust me!!!! use the proper oil. you only need 8lbs of pressure per 1000 rpm (minimum)

try cleaning the elbow that the oil pressure guage screws into out. it comes off the block with a littlew grunt work but it fixs the problem usually.

 

May I ask why you said 30wt is too thin? & recomend a multi viscosity?

this comes from someone that has used straight 30 for years in many cars. straight 50 or straight 60 weight in my Harleys, except for a month or so during extreme cold weather & then 20w50, & 20w50 in some cars, & either 10w30 or 10w40 depending on engine & condition. a fresh engine under 100,000 I try a multi viscosity, & see how it runs, & how much it uses, & how the engine responds. some cars like 1 oil better than others. my 93 Toyota truck prefered Penzoil 10w30, & I tried several, & it ran coolest & made best power. however my 86 Toyota, & 85 Toyota truck dont cars, nor does my wifes S10. my old air cooled VWs & MGB prefered 20w50

a well worn engine I would use either 20w50 or a straight 30 weight. I have a Toyota 1 ton that uses oil, & I use straight 30 weight, along with a thickening additive to help oil burning, even then I get 350 or so miles to the quart, but I have been doing that for the last 30,000 miles & I change oil every 5,000 miles. I would use 20w50, but it is hard cranking when I tried that, & I used the thickening agent as well, & only kept it in for a few hundred miles, so I went back to 30weight I cant think of name of thickening agent, but it is made by Rislone? I buy a few at a time & dont feel like going to look right now but if interested ask & I will see.

 

yea I thought the higher the number the thicker the oil was? like 90w gear lube. multi viscosity oil like 5w30 acts like 5w (thin) oil at low temps, then acts like 30w (thick) oil at higher temps. that was always my understanding....

 

my bad... i meant thick. you want more oil flowing to keep it lubed better. it helps it run cooler too.

 

Here's a really good site to learn about engine oil.. or rather, unlearn what you thought you already knew.

http://www.bobistheoilguy.com/motor-oil-101/