LOW OIL PRESSURE - PLEASE HELP.

2001 Jeep Cherokee, bought with bad engine. Removed engine, put one in from the junk yard. They said it only had 58k miles. Installed it, runs good but oil pressure drops to nothing after it warms up. Removed oil sending unit; checked with a mechanical gauge - same thing. Removed engine again; pulled oil pan, and removed cap bearings on crankshaft. Checked crankshaft bearings with plastic gauge - all were at .002. It seemed ok. Installed new oil pump - same thing. 45 lbs when cold and drops to 7 lbs when it warms up. Then gauge light comes on.

Frustrated and worn out. Please send help.

 

I have had the same problem for a long time and have learned to accept it. After alot of researching I found this to be fairly common on 2000 &2001 4.0s. Sometimes it is do to the cracked head issue destroying bearings but often times people like you have pulled their pan and found things to be in spec. Jeep did have some issues with botching cam bearings those years. Did you look up and see if one had walked out of its bore? Mine has even less than 7psi and I drive it every day,city and interstate. The check gauge chime used to bug me but I have tuned it out. I installed a mechanical gauge about 16 months so I could benchmark the pressure for future reference....pressure has not changed any since that time. Engine runs strong and uses no oil so I'm not too concerned.

 

Kind of the same problem happened today to me. NEVER have had a problem with oil pressure although the gauge seemed to move thee way it should. Pretty high when I start when cold then setles to the middle of the gauge when warm. Lwers a bit when idleing. Recent oil change kind of had me wondeing, as the gauge seemed to be a bit on the hig side. Then a recent trip, about 3 hours of freeway, about a steady 65 mph, the gauge slowly started to jerk itsef up to the top. Bounced around, back and forth..when backnto idle, it seems that the pressure is back to the middle of the gauge, but still boucing around?
Any suggestions for a cause?
04 cherokee, stock, 120,000 miles. Never burns oil so pretty confused by this.
Cherokeeinbc

Thanks

 

2004 Cherokees do not have gauges! It looks like a gauge but it is a dummy and will only read mid-scale when you have pressure and read zero when your pressure drops below 7psi

 

Hate to tell you but since I bought the Jeep new in 94, it has had a pressure gauge for oil in the upper right corner of the instrument display.
Been there since day 1 and I know after all this time I am not seeing things.
Did a but of searching....sounds like pressure sending unit?
Anyone? Bueller?
Thanks,
Cherokeeinbc

 

'94 had real gauges. I believe what he's referring to is the later practice of controlling the gauge readings with the pcm.
Chrysler got sick of customers thinking there was an engine fault every time the gauges moved. In response they started installing 'idiot gauges' that stay put with only token movement unless there is a gross fault. Upon gross fault the PCM slams the needle full high or low to get your attention.
In Chrysler's defense, most automakers do the same. Ford has done it for years with temp gauges, Toyota....Camry gauges magically never move off center, lol.

 

Yeah, people were a lot happier when cars only had idiot lights and they did not have a clue of what was going on in their engine!
When automakers started adding gauges their warranty claims jumped
because people who don't understand engines were getting freaked out. They complained about the readings being erratic or different than someone else's Jeep. So automakers kept the look but dumbed down the gauges and magically everybody was happy!

 

,,,,so getting back to my original problem,, that high reading on the oil pressure gauge that seems to have a mind of its own.
Oil pressure sending unit?

Thanks
Cherokeeinbc

 

It's a little less than courteous to hijack someone elses thread, especially when it's your first post. Be that as it may however, if you really searched you found that you can test the oil pressure sending unit with a DMM. You could always just buy one as they are cheap enough.

 

bobmarshall, i have seen threads with similar issues. try removing the sending unit run a line in to a clean bucket, run the jeep for a couple of seconds. see if any gunk comes out into the bucket, if so the hole for the sending unit was probably jsut plugged a little bit.

what is the oil pressure at 1600 rpms hot just out of curiousity??? what filter are you running? what oil and weight?

 

Heck, I was confused that an 04 Cherokee existed (OK, well, Patriot or Grand I guess)...I think now that it was a typo and he meant 94, not 04.

 

Just to help put this poor guy's thread back on track...

Do you still have the pan off? Perhaps check the oil pump screen? I've read where some people have run the oil pump with a drill to be sure it is pumping volume.

 

Thanks for all the help guys. Before I did remove engine I checked for plugged up oil adapter and ran engine without filter for a few seconds. Oil pressure at 1600 rpm is 12lbs with mech. gauge. I use 15-40 wt. oil, with a fram filter.

 

In my 4.0l my oil pressure gauge will go all the way up sometimes when I start it.... but after I get the engine up to temperature and shut it off then restart it the problem goes away?

 

What does the engine sound like? How does it run? does it smoke?