Oil Pressure on my 04 4.0 drops to nothing after reaching operation temps
11-03-2018, 05:44 PM
#1
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Model: Cherokee (XJ)
Oil Pressure on my 04 4.0 drops to nothing after reaching operation temps
I have a 2004 jgc Laredo 4.0 and the damn thing works great unless I have to drive it for more than 30 minutes, if I drive continuously for more than 30 minutes to an hour, then whenever I come to a stop and my rpms go down, I loose most if not all oil pressure. until I take off again or rev the motor in which case it’s just fine. Why would that do this. Don’t oil pumps go out in a bang and not gradually? Please inform me of wtf I gotta do.
11-04-2018, 05:42 PM
#2
Old fart with a wrench
Welcome to CF! Please change your profile to read 2004 Grand Cherokee (WJ) 4.0L. It will help with future posts.
It may be your oil pressure sensor. I say "sensor" because it's not a simple pressure switch, but a complicated digital chip-driven sensor. Pull out your wallet and buy a Mopar sensor, don't waste your money on an aftermarket piece of crap. I've already been thru this with my 2000 WJ. If you're not getting bearing rattle, you've got oil pressure.
It may be your oil pressure sensor. I say "sensor" because it's not a simple pressure switch, but a complicated digital chip-driven sensor. Pull out your wallet and buy a Mopar sensor, don't waste your money on an aftermarket piece of crap. I've already been thru this with my 2000 WJ. If you're not getting bearing rattle, you've got oil pressure.
Last edited by dave1123; 11-04-2018 at 05:48 PM.
11-05-2018, 06:33 AM
#3
CF Veteran
Its either you really don't have oil pressure, or you do and just can't see it. My guess is you don't. However on the long shot, much has been written about clogs of old oil getting in the passage way to the sensor, as well as bad sensors.
11-05-2018, 06:40 PM
#4
Old fart with a wrench
BTW, IDK if this is the place to say this, but I just switched from Valvoline dino 10W-30 to Rotella T6 5W-40 after 245K miles on the engine and I gained 5 psi pressure in all aspects of operation. That is, there's 5 lbs more at any temp or speed than there was before. Just though you'd like to know.
11-06-2018, 01:50 AM
#5
CF Veteran
BTW, IDK if this is the place to say this, but I just switched from Valvoline dino 10W-30 to Rotella T6 5W-40 after 245K miles on the engine and I gained 5 psi pressure in all aspects of operation. That is, there's 5 lbs more at any temp or speed than there was before. Just though you'd like to know.
11-06-2018, 04:45 AM
#6
Old fart with a wrench
At 210*, it's still holding 40 psi at idle. Almost 60 at 70 mph!
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11-06-2018, 09:58 AM
#8
Old fart with a wrench
Yeah, the one with 245K miles on it and a supposedly cracked piston skirt. Amazing ain't it? I switched to Rotella because it's supposed to be ashless when it burns so I thought I'd see if it fouls that plug less. My CCV oil separator is working perfectly. It pulls out about 1/2 cup of oil every couple of weeks. That's what was going thru the intake and carboning up the intake valves.
11-06-2018, 10:01 AM
#9
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You had a valve job on that and it still pulls oil into the catch can?
11-06-2018, 10:44 AM
#10
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Year: 1995
Model: Cherokee (XJ)
Engine: 4.0L
You can always hook up a mechanical oil pressure gauge temproarily to that port and see what's really going on. The Oil Pressure sensors on the 4.0L engines are a known weak spot they go out of calibration, leak, or just plain do wacky stuff and something as simple as hitting it during an oil filter change can damage it.
Aftermarket sensors are a waste of money. I've gotten them bad straight out of the box. I had one that would peg the gauge at RPMs over 3000 for some reason but would read normalish oil pressure at anything less. Dropped in a Mopar sensor that was about twice the cost of the SMP sensor and no more issues.
Aftermarket sensors are a waste of money. I've gotten them bad straight out of the box. I had one that would peg the gauge at RPMs over 3000 for some reason but would read normalish oil pressure at anything less. Dropped in a Mopar sensor that was about twice the cost of the SMP sensor and no more issues.
11-06-2018, 11:09 AM
#11
CF Veteran
BTW, IDK if this is the place to say this, but I just switched from Valvoline dino 10W-30 to Rotella T6 5W-40 after 245K miles on the engine and I gained 5 psi pressure in all aspects of operation. That is, there's 5 lbs more at any temp or speed than there was before. Just though you'd like to know.
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