i have a 98 xj and the oil pressure stays around 30 or a little below when driving and 10 when idling, is this common?

 

Acceptable range is 13-60.

 

It would be a good idea to check it with a mechanical gauge.

 

^^This is the first thing you want to do.^^
Also what brand of oil filter do you have on it? When I first bought my 98 XJ I had the same pressure as yours. It had a fram oil filter. I changed it out and put a Mopar brand and my pressure went from 10 at idle and 25 while diving. Up to 25 at idle and 45 driving.
I good brand filter will make a difference that is if you pressure switch is working correctly. Any ways it is always a good idea to use a good filter such as Mopar, Wix. Just don't use fram the 4.0 do not work well with them.

 

Wow ... good to know, mine does the same thing - sometimes when I'm crawlin the oil pressure will be around 10-15 & I'm thinking that's not good, that my oil pump is worn, maybe I should use a little thicker oil viscosity.
I'll try a different FILTER
I have replaced the sender AND put a gauge on it too - the in dash gauge pressure tracks right with the external gauge readings.

 

Mine has 5 psi at idle and 20-25 while driving and I drive it every day and don't worry about it. Low pressure usually means a worn engine so there is no magic fix......thick oil will make matters worse in the long run. You need flow,not pressure. Pressure is created by restriction as engines wear, clearances increase which decreases the restriction BUT increases the oil flow. If you are not ready to rebuild your engine I would just drive it and monitor it. The filter can cause low pressure so I would change that first.

 

For reference, here is the oil pressure spec for the Jeep 4.0 engine:

*Not less than 13 psi at HOT idle

*Between 37-75 psi OVER 1600 rpms

That being said, I have seen many 4.0 engines run for tens of thousands of miles with slightly less oil pressure at hot idle.

 

My '87 4.0 has 227k on it and it runs 10-11 psi at idle and around 20 while driving after it warms up. It's weird, the gauge reads around 45-50 psi when cold, but goes all the way down to 20-23 when it warms up. So far I haven't had any problems except a lifter tick that is kind of annoying.

I'd say drive it. There are plenty of guys on here with similar oil pressure and their XJs have run thousands of miles that way. The AMC/Jeep 4.0 was the one of the most reliable engines ever made.

 

It will be a good idea to check the actual pressure with a mechanical gauge first. The filter comment is a true one and also it is possible that your sending unit is failing also. Those are the two most common reasons for low pressure readings on the 4.0. I used to use Fram filters religiously and don't any more because of all of the issues I heard others having with them. Now, even though I sell Fram products, I have a hard time recommending them to customers for any vehicle.

I had a similar issue and it turned out to be a bad sender. Just in case you don't know the location of the sender, it is located right below the distributor. Easy access and easy swap.

 

Well hell then, no problemo ! It's pretty much normal . . .

Thanx