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Discussion Starter #1
Hello to all and glad to be apart of this site. I bought my first jeep recently, 2000 Cherokee Sport with 87k miles on the 4.0L

On the way home from buying it everything seemed to be running smoothly until I came to the first stoplight of the trip. All gauges were fine then all of a sudden my oil pressure dropped to zero and my temp rocketed to 260+

I got through the light in a panic and built up speed, everything returned back to normal (oil 40+, temp 198-200). I came to stoplight #2 and it did the same thing, like instantly.

The engine didn't knock or tick and it didn't idle rough or anything.
The previous owner changed all the sensors and switches, the electric fan comes on fine and the main fan sounds like a freaking hurricane so I know it's working.

I called the previous owner about this and he said it did it all the time and never caused a problem so he just ignored it. He bought the jeep new and said it started about 2yr after.

Any tips or suggestions that might help? Thank you, Brian.
 

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Seeing how you say that the mechanical fan sounds like a hurricane I wonder if somebody put the ZJ fan clutch on the Jeep.
Then we have to wonder what brand sensors were used.
The general consensus is we use Mopar ones and nothing else for most.
First question is do you have your shroud around the mechanical fan?
If so I guess if this were me I would start with the fan clutch.
When hot if you shut off the motor the mechanical fan should stop spinning within a second or two.
If it just spins usually an indication of a bad fan clutch.
Also you will want to put a mechanical oil pressure tester to the Jeep.
See what that says. Now you will want to let her idle for a long time cause you really want to know the pressure
reading at a very hot idle.
Also you might want to give that hole that the sensor goes into in a cleaning.
Sometimes it is gunked up.
I would start with that.
When I finally got around to checking my '00 with a mechanical oil pressure gauge, for no reason other then curiosity,
I got the bright idea to plumb in some fittings so I could run the sensor for the cluster gauge and the mechanical one
at the same time. Wanted to compare the readings for both of them.
That shot of the gauge is at a very hot idle and pretty much read what my cluster gauge read.
 

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Hi, yes the main fan stops spinning almost immediately. That's a great tip about the oil gauge.

It's really strange because both gauges go berserk at the same time and it doesn't happen slowly, they just pin instantly then the "Check Gauges" light comes on too.
Thanks, Brian.
 

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Hi, yes the main fan stops spinning almost immediately. That's a great tip about the oil gauge.

It's really strange because both gauges go berserk at the same time and it doesn't happen slowly, they just pin instantly then the "Check Gauges" light comes on too.
Thanks, Brian.
One thing I did forget to mention is grounds.
With it just happening when at a stop light makes it maybe not.
But it is one thing that you should check regardless.
Google will give you plenty to read about concerning location.
And this is not a just look at them thing. Take them off, clean them up, and a put it all back together thing.
Then wiring to the sensors.
Electric is not really my thing but maybe something is grounding out and causing the sensors to do what they are doing.
Hopefully somebody else will chime in.
Back to just at the stop light thing seems weird though.
Any chance you know how it reacts if you put the Jeep in park and take your foot off the brake?
 

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Discussion Starter #5
It does the same thing parked in the driveway at idle. Everything will be fine for 10 minutes or so then bam!,
the oil drops to zero and temp pins.
 

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It does the same thing parked in the driveway at idle. Everything will be fine for 10 minutes or so then bam!,
the oil drops to zero and temp pins.
I asked that cause I wonder if hitting the brake had something to do with it.
Shorting out something maybe.
Please realize these are just all guesses.
Just out of curiosity happens in the driveway from a completely cold start within 10 minutes?
It think we need to find out what the oil pressure is with a mechanical gauge, idling in the driveway, at a very hot idle first.
 

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Discussion Starter #7
Ok, I will go to O'Reilly's and see if they can set me up with something.
I wonder if I should just go with mechanical gauges anyway?, seem more accurate and dependable.

It runs fine down the highway though, it's crazy!
 

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Ok, I will go to O'Reilly's and see if they can set me up with something.
I wonder if I should just go with mechanical gauges anyway?, seem more accurate and dependable.

It runs fine down the highway though, it's crazy!
That is why in my first post I wondered exactly what sensors the PO had used when he replaced them.
In my '00 all of a sudden my oil pressure gauge was pinned.
While not a good idea to shoot the parts cannon at the Jeep was pretty sure the sensor just crapped out.
I did go against the grain and use a Napa one. The Echlin line one. But I work there and blah blah blah. LOL.
Anyway been 4 maybe 5 years now so far so good so.
But mine pinned and stayed pinned.
Not just when driving or at an idle so.......
 

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There is so much going on after the engine heats up. I agree with Ralph. Check your grounds at the engine block, you have one on the fender and one at the firewall. Also, maybe pull your gauge cluster and remove the electrical connectors and reinstall them. Since the gauges go bonkers but the engine is operating "normally" it may just be a bad connection.
 

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Oh any chance you have a IR thermometer?
Cause figure when you are playing with checking oil pressure should shoot the thermostat housing to see what you see.
That should have occurred to me earlier. Sorry. LOL.
 

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Discussion Starter #11
Great information guys I really appreciate it! I will start on it today after work. Thanks, Brian.
 

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The more I think about this.
Check the grounds first. See what happens.
Check your belt while you are at it. This is just concerning cooling.
You are going to have to use the "yeah that looks about right" method cause guessing you don't have a belt gauge.
Cause that is one thing I discovered about my '00. More picky about belt tension.
My '96. Eyeball it and good to go.
So we do that, see what we see, and go from there.
 

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Hello to all and glad to be apart of this site. I bought my first jeep recently, 2000 Cherokee Sport with 87k miles on the 4.0L

On the way home from buying it everything seemed to be running smoothly until I came to the first stoplight of the trip. All gauges were fine then all of a sudden my oil pressure dropped to zero and my temp rocketed to 260+

I got through the light in a panic and built up speed, everything returned back to normal (oil 40+, temp 198-200). I came to stoplight #2 and it did the same thing, like instantly.

The engine didn't knock or tick and it didn't idle rough or anything.
The previous owner changed all the sensors and switches, the electric fan comes on fine and the main fan sounds like a freaking hurricane so I know it's working.

I called the previous owner about this and he said it did it all the time and never caused a problem so he just ignored it. He bought the jeep new and said it started about 2yr after.

Any tips or suggestions that might help? Thank you, Brian.
Hello, I had this same problem with the low pressure at idle. It is actually a simple fix. Take the pressure sensor out and run a pipe cleaner or qtip threw the hole. Oil gets clogged in the hole that gives a false reading on the sensor. As far as the over heating, get a 3 row radiator, mine never overheated again. It could also be a cracked head.
 

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Discussion Starter #15
Man I hope it's not a cracked head😬
I checked down inside the oil fill spot with a light and didn't see any of the telltale discolored cracks or any moisture of any kind but I guess that means nothing really.
 
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