Hey guys, just looking for the normal oil pressure for this old 4.0? It's running around 20psi for the most part, give or take a little when cold or hot. Thanks.

Sounds like a sending unit problem. My opinion is that is too low for all day running.
I betcha a new sender will fix the pressure.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Are you using the right oil? Changing it regularly? 4.0 specs are 13psi @ idle and 37psi at 1600 rpm or above. I agree with Jim I'd change the sender first. Get a second opinion so to speak. <img src="/forums/images/graemlins/cheers.gif" alt="" />

yep i agree,and if that dont help try a little heavier oil. that is what im going to do next oil change. at the current time(with new sender unit) it is 40 when cold and drops to 20 when hot(@ 2500 rpm or so).im currently using 10w 30 im going to jump to 10w 40 and see what happens.
likely like mine it is pretty worn(mine was abused by the previouse owner) leaving a bit more wear. a slightly heavier oil can take up the space and make it run as it should,or close to it anyway. oh i almost forgot the book we have at work actually says chrysler recomends 20w 50 but im not sure i would try that yet.

Thanks for the quick answers guys. I bought this thing about a year ago with 160K on it. I don't think it was beat on intentionally as in driven hard or offroad, in fact I doubt it ever went offroad, but who knows how it has been maintained and it may have gotten beaten just by being treated the way 75% of people "take care" of their cars, if you know what I mean.

It was a daily driver for an older women who drove it about 20 miles a day, to and from work, for the most part, her husband claims he always had it professionally serviced, but I can see a decent amount of sludge up in the valve cover, on the rocker arms, then again it's 20 years old. It sat for about a year before I found it, I put a starter in it and it started right up, once it ran for a while I found some other minor things wrong and fixed them, a new coolant bootle, replaced all of the PCV lines, some brake work, and the distributor was cracked at that little ear that comes off it to hold it down, as well as the hold down fork being cracked in half, so it was leaking oil pretty bad from there. Pulled the dist. welded the hold down ear back on and got a new fork and gasket, and it's good as new, no leak at all and nice and tight now.

I have put about 1,000 miles on it since I got it running, and it has given me no problems at all. I always kind of thought the oil pressure should be higher and then a couple of weeks ago I was in a brand new Wrangler with a 4.0 and noticed the pressure was much higher and also fluctuated from idle to any higher RPM, mine just sits at 20psi all day long, maybe drop a little when it gets real hot in traffic in the summer, but mostly sits at 20. I am using 10w-40 in it and haven't changed it yet since I have only put 1K on it. I would never use 20w-50 in any car, it's just way too thick to get where it needs to be.

I will replace the sender on it first and see where I'm at. There is plenty of oil running all over the rocker's in the head when I look through at idle, so I'm assuming I have decent pressure, but I guess I'll find out when I replace the sender. Should I see fluctuation from idle to higher RPM? Thanks.

I see plenty fluctuation with engine speed after it's warmed on my 93. If it's not fluctuating at op temp, good chance it needs a sender. <img src="/forums/images/graemlins/cheers.gif" alt="" />

hey there i have a 90 jeep xj with the 4.o and it has 216k miles and i have low oil pressure too. what should i do to make it higher??? or what could be the problem??

Rebuilding the engine wouldn't hurt.

How low is it and did you read the rest of the posts in this thread? <img src="/forums/images/graemlins/confused.gif" alt="" />

you can always try dropping the pan and putting a high volume oil pump in it helped my cousins wrangler that had low pressure also a heavier oil wouldn't hurt