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OIL PRESSURE PROBLEMS

2

2001 RED XJ

NAXJA Forum User
Location
Flora,IL
I replaced my sending unit saturday because my gauge has been all over the place. It went down to 0 and the light came one. I replaced it but seem to have the same problem but not as bad. What else can it be? Could the gauge in the dash be bad? What is the symptons of a bad oil pump?
 
The first thing you should do is to check the dashboard gauge/oil pressure sender accuracy. Install a mechanical oil pressure gauge.
 
Tim_MN said:
The first thing you should do is to check the dashboard gauge/oil pressure sender accuracy. Install a mechanical oil pressure gauge.
Click to expand...

Agree with Tim. You must verify. And that has to be done with a mechanical oil pressure gauge, installed where the oil pressure sending unit resides.

Many parts stores will rent you a mechanical oil pressure gauge very inexpensively; call around for availability.

Use a testing based strategy to lead you to the "root cause".

Good luck and keep us updated!
 
Last edited:
Yea, Tim is right, check with another gauge. I personally don't think the oil pump is bad, unless some weird failure occurred. Usually it drops pressure gradually. I'd also look into how the electric plugs are, cleaned, proper solder/connection, etc. You could also try another sender. Could also be a short or bad "imperfect" contact somewhere.
 
x3 on the mechanical gauge. If it still shows low oil pressure, then you should worry.

Minimum is 13 PSI at an idle, according to the owner's manual, although many will tell you that 10 PSI for every 1k RPMs is fair too.

Does your engine make any knocks?

If all else fails, you can always pull off your oil pan and replace rod and main bearings to see what happens.
 
When I start at cold engine it goes up to 50PSI. When motor gets warm it gradually drops and when I come to a stop it goes to 0 and the gauge lite comes on.
 
Your PSI at a cold idle is irrelevant and isn't going to help with a diagnosis, so just keep that in mind. Also, all oil pressure goes up when moving parts start moving more, so that probably won't help either.

The point at which you need to troubleshoot is at a warm (210-degree) idle. Your oil pressure at that temperature, at an idle, is all that really matters.

You saying that you have no knock is a good thing. So I would start with a mechanical gauge. With this, you can verify whether or not the factory gauge reading is correct or not. Very often, the pressure sending units go bad on these Cherokees, and a mechanical gauge will tell you if it did or not. If you don't have a mechanical gauge, then just go to Advance Auto Parts and get a new oil pressure sending unit and put it on and see if it solves your problem.

If your pressure sending unit isn't bad, you can always try using a different oil or a high volume oil pump. These won't cure oil pressure problems, but they can help hang you over where you need to be temporarily until you have a mechanic check out all of your main, rod, and camshaft bearings for wear.
 
Oil typically takes a lot longer to heat up than coolant. Test with a mechanical gauge. If it's good, you have a sending unit, wiring, or gauge problem. Normally the problem is a bad or defective sending unit. Dealer sending units usually work the best, the first time. I have a NAPA Echlin on my 01 XJ and it works fine, but on my 97 XJ after 2 tries with the NAPA Echlin, I got a refund and used the dealer one. With yours being an 01 XJ, it is possible your engine truly does have low oil pressure from a bad heading leaking coolant into the oil and washing the bearings, etc.
 
You can do that. If it doesn't help, do the mechanical gauge test. If money is involved, i.e. can't rent a mechanical oil pressure gauge, then try a dealer part, or try a NAPA part (but save the box for return if it doesn't work).
 
Last edited:
If you already replaced the sending unit and it's still bad, then your problem is mechanical. You likely have bearings out of spec from wear.

Next thing you can try is a slightly thicker oil or oil additive.

If that doesn't work, run the engine till it blows... Because you've got bearing issues that will lead to a rebuild. If you have a cracked head like others are saying, be prepared to buy a new head too.
 
There is no screen. Honestly I think you need to spend less time asking questions and doing so you find some resolution quicker. Remove the elbow and make sure its clean. Then mechanical oil pressure gauge is your best bet followed by a dealer sending unit, because aftermarket sensors are notoriously suspect. If the mechanical gauge shows low after the elbow is cleaned, then you have a mechanical rather than electrical problem frequently caused by bad mains and/or cam bearings. Lots of people change oil pumps when they have the pan off, but I can't see a reason to do it unless there's a problem such as a clogged screen or it just died. On your model year the heads crack and leak coolant into the oil which washes the bearings. Once that happens you either run it until she blows or replace the mains and cam bearings, or get another engine.
 
My MJ has the same issues. I have been driving it since June like that. It has not gotten any worse and it seems to be doing ok. I replaced the oil pump a few years ago and changed the sender also because of the low oil pressure issue. I sold the truck 4 years ago with the same issue and it was daily driven 50 miles a day. I bought it back in June with the same problem. No oil pressure at idle. I have a spare motor waiting for this one to blow up but I still haven't needed it. I think it may be a blocked passage to the gauge sender. I just haven't felt like trying to figure it out. I say if it isn't knocking, run it.

And yes I have a 97+ swap done to my MJ.

10509749_10202972341176602_8881068838691670033_n.jpg
 
Pull the pan and check the punp and bearings. Get a good used engine at the junk yard if the bearings are shot unless you plan on doing a full rebuild. Or Live with it until the engine dies.
 
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