SCarolinaXJ

I just bought a 2001 XJ with about 200k miles. I've put maybe 50 miles on it...drove it to a buddy's house to put in the lift kit, then to the tire place to put on my new wheels and tires. This is going to be my off-road rig.

Today I made a run to the store in it and when I started it in the parking lot, the "check engine gauges" light came on and my oil pressure gauge was at zero psi. I shut the engine down, looked for leaks and after a few minutes checked the oil level. The oil (recently changed) was still at the full mark on the dipstick.

I started it up again, the oil pressure went up to about 10 psi and stabled out at about 20 psi on the road as I gently drove it home. In the driveway at idle, it indicated ZERO again and I immediately shut it down. I don't recall what the oil pressure was before. The only things I've touched on this rig is the suspension, tires and I put on aftermarket bumpers.

My thoughts are:

- bad gauge or bad sending unit (hopefully), although it did indicate oil pressure was rising and falling with RPM, between 10-25 psi while driving.
- bad oil pump
- clogged oil pathway

Last time I dealt with an oil pump on a car it was in the oil pan, driven by the distributer shaft. I don't even know where it is on a Cherokee.

Any ideas on what's going on here?

kstopp

I would suggest replacing the oil pressure sender first, as they are known to fail and fairly cheap. Or if you are on a budget, you can replace the sender with a mechanical gauge to temporarily check for oil pressure, then if the sender is at fault replace it.

SCarolinaXJ

Where is the sender unit (obviously time for me to get a Haynes/Clymers)?

Radi

^^

The pressure sender is a common failure. More often they fail by reading high, but low or zero happens to. While you have it off, clean out the feed passage too, just in case.

Any noises that would indicate bad oil pressure? Valvetrain/lifters?

jaygitt82

start by making sure your not losing antifreeze. the 0331 casting heads are prone to cracking and your oil pressure to slowly drop while the motor is warming up. if thats not your issue check your connection on the oil pressure sending unit its right next to the oil filter 1 1/8 size wrench will take it off(its brass color). other then that start with the pressure sending unit. and the oil pump is in the oil pan fyi. its about a 3 hour job. not hard just some time

RTorrez1

The first thing you should do is VERIFY the oil pressure. Go to the auto parts store and rent a mechanical oil pressure gauge. Also what oil filter are you running?

SCarolinaXJ

For what it's worth, the engine sounded normal. It has a Fram filter on it...the previous owner said he recently changed the oil, and the oil looks new.

Now that I know where the sending unit is (thanks), I'll take a look at the connections and coolant level (easy fix first) and take it from there. It's possible I bumped something while I was under the Jeep doing all the other stuff. If it's not an electrical connection, I'll find a gauge to test the pressure.

What's the "normal" pressure for this engine? I would guess 20 psi at idle and 30-40 at nominal driving speed.

Thanks for the help, I'll let you know what I find out.

cruiser54

Get rid of the Fram. Soon. They are known for causing low oil pressure problems on the 4.0. Wix or Napa Gold. Or, Mopar from Walmart.

jebmccall

frams are known as orange cans of death and are related to causing low oil pressure.

oil pressure spec is minimum of 13 psi at hot idle, 37+ psi above 1600 rpms when hot.

also worn rod and main bearings can cause low oil pressure. if the crank is not grooved you can get away with just putting bearings in if that is the problem. but verify you're pressure and report back first.

Firestorm500

Busted head and wiped bearings from coolant contamination would cause that.

PO might have changed the oil just before selling to hide milky oil.

I hope it's just a bad sending unit.

SCarolinaXJ

Thanks for all the replies, I finally got time to dig into this and fix it. I couldn't find anywhere to rent a pressure gauge, so I decided to just start with an oil change. At least then I would be dealing with a known good filter and known good oil.

The Fram filter was seriously torqued on there. I had to use a filter wrench and I still ended up crushing and ripping the metal on the filter before it broke loose. I cut the filter open and it was full of black murky sludge. My guess it that since the filter was on so tight that the last guy just changed the oil and didn't change the filter. It's possible that the guy before him did the same thing.

Now I have 30 psi at hot idle and about 50 psi at 2500 RPM.

Thanks again for the help.

Firestorm500

Great news.

You might want to change the oil again in a couple of thousand miles after the new filter has caught some more sludge.

SCarolinaXJ

Good idea. That, plus with this rig being used almost exclusively off-road, those will be some hard miles.

cruiser54

Perfect. Like stated, do another change sooner than later.