Well I just picked up a 92 Cherokee with a 4.0. When first started the oil pressure is around 40. After a few miles when it gets up to operating temp it is around 15-20, at crusing speeds, when getting on the gas it is about 25. When coming to a stop it drops down to zero.

I was told to take the valve cover off and check to see if the drains are clean, they said it may be clogged up and not leaking back down to pan.

I dont think its the oil pump because pressure is high at first. Any ideas, thanks for any help that you can offer.

 

I would change the oil and filter with some quaility oil and filter and change your oil pressure sending unit! They placed the sending unit in a bad spot (right over the oil filter) and alot of people have damaged or snapped it off when removing the oil filter.

Hope this helps

 

X2 on trying good oil and filter first,also try checking the wire comeing off the sending unit it gets pretty crispy,so it could be shorting out.

 

Ok will do, how much is the unit? and how hard to install?

Thanks for the fast reply!

It has 233k on her

 

they are around 30 bucks give or take,and supper easy to install.Just unplug the wire and unscrew it.

 

Also, there looks to be some leaking on front and rear diff, I know I need to check it but not sure how, what about on the trans. case fluid?

 

try replacing the sending unit first. could be a bearing issue. i know i had a wiped crank bearing that cause oil pressure to drop to 0

 

There are large plugs on the front of the diff cover. U need to use a 3/8" extension to un-screw it as it is square inset. The proper fluid level should be just at the bottom of the inspection hole. Your trans case has to large plugs on the left side I believe. the top one is your inspection hole and your bottom one is the drain hole to change the fluid. If you just bought this, I would spend the money and buy all synthetic fluids and change then all (Oil, diff fluid, trans fluid, t-case fluid.) I changed all of mine over to Mobil 1 synthetic. It will be a very good investment.

 

Thanks guys everyone is really helpful here

 

Yeah this place is a life saver!! Use it well and become a supporter of this site!

 

I just put some pictures up on in the Introduction forum if you guys are interested.

 

Well good and bad news. I replaced the sending unit, did an oil change with 5 qts. valvoline max life 10w40 and 1 qt Lucas oil stabalizer. With a new oil filter (purolator)

The oil pressure doesn't go all the way 0 anymore, it is at 5-10psi when idling.

My next thought is a new oil pump. What do you guys think?

 

There is a post somewhere that breaks down what filters are made of. You should try a MOPAR filter before you try oil pump. I THINK (and seasoned members, correct me) adequate oil pressure is 10psi for every 1,000 rpms...I'm not sure though. When your driving at speed and normal operating temp, what is the gauge reading after the new pressure unit? You may also want to try an aftermarket oil pressure unit as those are typically more accurate than stock ones due to where the stock ones are located. Just a thought.

 

When cold it is around 30-40psi while driving, when hot around 20psi give or take.


I haven't heard any knocking or any noise for that matter when it even got down to 0psi. Hasn't hit 0 since the oil change/sending unit.

I have been searching seems like this is pretty common on 4.0's....

 

From what I hear lucas is kind of like a bandaid. What do you think the most qts of lucas I should use out of. Should I switch to straight 40 wt?