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No Oil Pressure

A

alexarp

NAXJA Forum User
Location
Dallas
I have an 01 with a 4.0. When cold, pressure sits at 40psi, but after everything heats up, I have no pressure at idle and the check gauges light pops up. I bought it with 147k eight months ago, and it always ran over 40psi at speed. The issue started yesterday and after a few google searches, the two issues that have came up are the sending unit and a cracked head. I've read that the sending unit is a cheap fix but the cracked head sounds expensive. Is there anyway I can figure out the issue myself? I've never used any type of forum but any advice would be very appreciated.
 
I would be suspect of the sending unit, easy fix.
if the engine was running with no oil pressure it would start to knock.
fyi the sending unit is right above the oil filter, bout 20 bucks @ oreillys
 
Have you been having to add antifreeze to the coolant reservoir? The reason I ask is that a common symptom of a cracked 0331 cylinder head is "unexplained coolant loss".

I'd start though by verifying pressure. Rent a mechanical oil pressure gauge and temporarily install it where the oil pressure sending unit resides. Compare the readings from the mechanical oil pressure gauge to what you're seeing on your dash.

The oil pressure spec. for the 4.0 is this:

*Not less than 13 psi at HOT idle
*Between 37-75 psi OVER 1600 rpms

Good luck!
 
I've got a Y2K XJ with a 0331 head, so I'm living in fear of the ticking time bomb of the head cracking. Based on what I've read, the advice above about the unexplained coolant loss is THE big indicator along with the residue one the oil cap and/or radiator cap.

You're saying that you're noticing the lack in oil pressure while you're driving, so I'd assume that means that you're checking your gauges regularly while you drive. That SHOULD mean that you'd also notice if your engine temp is running hot, but if not, be sure to check that too. I think normal is right at 210. Higher than normal temps would be another big, bad sign of a cracked head.

Just in case though, I'd STOP driving it until you can replace the sending unit (if it's only $20 to replace, hell, it's worth a shot, right?). If you do end up having to replace the head, trashing your bearings by driving it with that cracked head is only going to make that little "project" more expensive.

Good luck! And be sure to keep us updated.
 
The key is that the light says "check gauges" not "check engine"...is there a code??

Check gauges means sender or gauge, likely the sender as said.
 
First thing first. If you are running a Fram filter, get rid of it.
 
Is a quickie lube joint changing your oil?
What weight Oil are you using? 10W30 is recommended.
The reason I ask is that I have seen quickie Lube places put 5W20 in everything, In most cherokee XJ's 5W20=very low to "0" oil pressure.
 
garr said:
Is a quickie lube joint changing your oil?
What weight Oil are you using? 10W30 is recommended.
The reason I ask is that I have seen quickie Lube places put 5W20 in everything, In most cherokee XJ's 5W20=very low to "0" oil pressure.
Click to expand...

Yep and the sticker says they used 5W30.

Thanks for all of the replies. Noticed coolant leaking onto trim underneath the radiator on the drivers side today. Hopefully that explains the loss of coolant. Also prayin the sending unit will take care of the oil pressure. Taking to mechanic tomorrow to have coolant system checked out. Is the sending unit something I can pick up at local parts store, and if so is it an easy DIY install?
 
ParadiseXJ said:
The key is that the light says "check gauges" not "check engine"...is there a code??

Check gauges means sender or gauge, likely the sender as said.
Click to expand...

Yes, the check engine light came on mid july of last year. Took it to a lube place and code came back as a cylinder misfire. Did some research on the symptoms, would run rough on warm start in the heat of the summer. Read threads about putting heat deflector over cylinder 3 or 4? fuel line to solve issue, but i never did anything with it. So hopefully your right about the difference b/n check gauges and engine light.
 
alexarp said:
Yes, the check engine light came on mid july of last year. Took it to a lube place and code came back as a cylinder misfire. Did some research on the symptoms, would run rough on warm start in the heat of the summer. Read threads about putting heat deflector over cylinder 3 or 4? fuel line to solve issue, but i never did anything with it. So hopefully your right about the difference b/n check gauges and engine light.
Click to expand...

Joke--that "fix" for the number 3 injector.

The problem is "hot soak" or "heat soak"--TSB 18-031-03 of Sept. 5, 2003. The factory "fix" is the shielding of the number 3 injector, and it is no fix at all.

You have to reduce the underhood temperatures--install an electronic timer in the efan circuit that will run the efan for 5 minutes after the ignition is shut off.
 
Re: engine oil pressure.

You can try a new sending unit, or use a mechanical gauge first to determine if the problem isn't in the engine.
 
Sidewinder CC said:
Why?
Click to expand...

5W is too thin in a Truck engine like the 4.0 (Unless you are in sub-zero climate), My 40 years of experience with the engine shows leaks & low oil pressure with thin oil, Especially 5W30 non synthetic, 5W-30 synthetic seems to leak a bit, but the pressure hold up better, Not as good as 10W30-40 but better.
And I am talking about leaking in a well maintained truck with No Leaks otherwise, The thin oil just seems to slip by the front part of the oil pan gasket, Not much, but enough to see it on the pan, If I use a 10W30 there are no leaks, This has happened to the 5 4.0 equipped jeeps I owned over the years & an old 258 equipped CJ7 also.
 
... I've been running 5W30 in my 4.0s for literally years and never had a problem. And the manual says you can use 5W30 in the summer. If you have leaks you have crummy seals.

If you aren't getting horrible rattling from the valvetrain when it reads 0psi or drops low, you probably have a bad sender. Replace it and see what happens.

Also check for milkshake on the dipstick and oil fill cap, and unexplained coolant loss, but I really suspect a sender if you've got no other symptoms.
 
ParadiseXJ said:
Check gauges means sender or gauge, likely the sender as said.
Click to expand...

The "Check Gauges" does not mean that it is telling you that there is a problem with the gauges or the sender themselves. What it means is that it wants the driver to look at the dash. When the check gauges comes on the cluster also pegs the gauges with the suspect reading to 0.
 
kastein said:
... I've been running 5W30 in my 4.0s for literally years and never had a problem. And the manual says you can use 5W30 in the summer. If you have leaks you have crummy seals.

If you aren't getting horrible rattling from the valvetrain when it reads 0psi or drops low, you probably have a bad sender. Replace it and see what happens.

Also check for milkshake on the dipstick and oil fill cap, and unexplained coolant loss, but I really suspect a sender if you've got no other symptoms.
Click to expand...

I can only speak from my experiences.
I had the wife’s brand new 4.0 1994 GC leak after the 1st oil change @3000Miles, She took it to Jiffy Lube & they put dino 5W30 in it, the oil pressure was also on the low side. I changed it to M1 10W30 & No more leak + Higher pressure, Did not leak anymore right up until the day I sold it (@ around 80K miles).
 
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