dirtsurfer7

hey folks im an oldschool jeeper just bought an xj, last jeep i had was a 56 ****** wagon so im a little new to these xj's. anyway i have changed the oil in it cause it was due, didnt know what grade of oil was in it so i put 10 30 in it, a day or two later i noticed the oil pressure actually fluctuates with engine RPM, idles at 20 psi and go's up to 45 psi at the highest rpm, anyway before it just stayed at 40 and never moved and now it moves with more rpms as you would expect it to with a normal gauge, granted anytime you have an oil pressure gauge on a stock dash theyre not that accurate, but i just wanted some feed back, is this normal for the 4.0, by the way its a 2000 with 130,000 on it, any feedback would be awesome.

illicit

Yeah!! Thats completely normal.. No need to worry.

popo8

Oil pressure should move with RPMS. Actually I believe the math is 10psi per 1,000rpms.....

as long as at idle your not going to 0 and at WOT your not pegging the guage, your fine....

dirtsurfer7

yeah ive never had a mopar jeep but heard alot about them, thanks guys, i guess im just used to my cj's with small block chevys under the hood

popo8

well that idle/oil pressure math should be with any motor... from my stroked chevy 2 my 3.0 v6 montero

dirtsurfer7

yeah and ive always known that, i guess what threw me off was it didnt do it at all before the oil change, before i changed the oil it stayed right at 40 psi and i just wanted some outisde input

popo8

thats cool, and if your sure it was not doing it prior, you may want to check your sending unit, because it may be on its way out and you may find yourself in trouble when its reading 40 and there is nothing, or when it reads nothing even though everything is fine and you have a coronary...

zedpapa

the rule of thumb on oil pressure is 10 psi per 1000 rpm. my jeep idles at 20-25 psi and maxes out around 50-55 psi at 1800 rpm.

zedpapa

X-J

When the oil is cool the pressure will be high untill it warms up and thins out , then your pressure will fluctuate with RPM.
Electronic gauges will not show the pressure fluctuation as quickly as a mechanical gauge, when my in dash electronic gauge died I installed a mechanical gauge to keep a closer eye on oil pressure.
hope that helped.

firstime00XJ

I've got a 2000 XJ too, and when I put fresh 10w30 in it, mine did the same thing. It is normal. I just did another oil change and put 10w40 in it, and it idles at 30-40psi and runs about 50-55psi at 2000rpms. (around there, I'm estimating)