2000 4.0 overheating at idle and in low gears

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oldgray

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Mar 16, 2019
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Here's the list:

gauge acting weird, spiking up to 210 then 260 within seconds then leveling out a couple minutes later when no longer idling/ higher than 3rd gear.
3rd gear seems to be particularly problematic. Has had the CEL come on but it's currently not.

I replaced the radiator about 3.5 years ago but it blew again a couple weeks back after the gauges started going haywire. ( Pretty sure it was a loose rad cap at this point but unsure) The engine didn't act like it was over-heating, it honestly seemed like a faulty gauge /sensor.

It's dead of winter in northern Utah with two jobs means no time for repairs. I had the shop replace the radiator, (now worried they installed a sub-par rad) and a week or so after that, going about 20-25 and downshifting to a stop on residential streets, jeep just dies completely, all gauges gone, no response from battery or engine, no turn-over, nothing. Battery is fine, all lights worked and tested it. Had it towed back to the shop to see what they messed up. They claimed a section of wiring in the passenger wheel well was faulty/corroded. This is after I told them about some other corroded wiring issues I had when I bought it. Hate taking it to a shop as I'd rather have the peace of mind knowing what's being done in my vehicle.

Anywho, after all this, my gauges are still reading hot when idling and in lower gears but not at freeway speeds, it typically reads right in the middle at freeway speed and will even go back down after shooting up and sending the "check gauges" light.

Any idea what might be causing this? It runs the same when the gauges are going wacky so I'm not sure that it's actually overheating but my thoughts have gone to :

CTS
fan clutch
thermostat
water pump


Has anyone had similar problems or direction with what to do next? I want to try what I can while it's warm and not snowing this week before I bite the bullet and take it back to the shop to have them "fix" it.
 
When the CEL was coming on, what codes what it throwing?

Also, try scanning it now and see if it has any stored or pending codes.
 
I'd certainly replace the thermostat for starters. It's a cheap part and is a common culprit . It was the issue with the overheating in my 2001 4.0, though it overheated regardless of engine speed.
 
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TJ Hunnicutt said:
I'd certainly replace the thermostat for starters. It's a cheap part and is a common culprit . It was the issue with the overheating in my 2001 4.0, though it overheated regardless of engine speed.
Click to expand...

I also had some eratic variation in my temp gauge, never overheat or anything but it seemed like it was having trouble fully opening. Stant thermostat swapped in and no more issues.
 
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2 1/2 hrs into 3 hr drive in my 03 Rubi; temp gauge goes into red zone & light comes on. Pull over, check AF-OK, serpentine & water pump; no issues. Start engine after 2 minutes; back in normal zone. Finish drive. 3 hr drive home & watching temp gauge: occasional brief creep into red zone with two issues of warning light coming on. Gauge goes back to normal.
Any thoughts? I'm thinking sticking Tstat?? Or new radiator.

Also noticed transmission temp (I have a gauge reading pan temp) is also fluctuating between 180 & 200which is new. Related?
 
My first guess would also be a sticky thermostat. Can't see how the radiator could cause fluctuations...just getting too hot, yes, fluctuations not so much. Also, when was the last time you did a flush? Would want to eliminate the possibility of crunchies in the system being a problem.

As for the tranny also fluctuating, it's entirely possible, since the tranny cooler is in the radiator. I assume that the fluctuations coincide with those of the coolant temps?
 
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