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My daughters 2004 Grand Cherokee (4.0) a week ago Friday threw a code - said Thermostat, so I replaced the thermostat, OEM 195, easy job. Drives for a week all is fine. Last Friday it overheats - she has it towed to my house. No leaks, system is full, pressurized, all looks fine. When she bought the car 3 yrs ago it was loaded with stop leak, which I told her was a big concern but it was too late. But that was 3 yrs ago and it's been fine. My first thought is that when I changed the t-stat and replaced a lot of coolant that it stirred stuff up inside and maybe the t-stat was stuck. Took it out, looked fine, put it in water, heated, it opens fine, etc, cabin is smokin hot, etc. Reinstalled t-stat, new gasket. On to plan B - radiator, was original, and with all the stop leak thinking ok that has to be clogged and the problem. Replaced it yesterday, refilled the system again, still overheating. Water pump is only item left , showing no signs of being bad, not weeping, pulley is true, no noise, but replaced it anyway. Refill again, STILL overheating. UUUUGGHHHH......

I do not think it's a head gasket as shows none of the expected signs such as exhaust vapor, no coolant in the oil (its clean), no oil found leaking, idles fine, starts fine. Not likely a temp sensor as that would throw a code and there are no codes. Now - the only thing I've noticed is that the electric fan doesn't seem to be turning on until it's pretty hot past the 195 -210 operating range, and I don't know if the fan is functioning at full capacity as it's not my car, but the fan is essential to cool if just sitting idling but would that alone cause an overheat? There's nothing left as there are not that many moving parts to a cooling system. Again for the past 3 yrs the car has been fine - no issues, and even a week after t stat change.

Would REALYY APPRECIATE and insight here as I'm at wits end on this one. The only good news is it's easy to work on, but I'm tired of working on it.

THANKS!
 

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2019 Jeep Grand Cherokee Trailhawk
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Sounds like you’re going down the right path. Personally I would think about what’s causing the overheating. Is it under certain conditions, long drives, short drives, hot vs cold days, etc.
Last time I worked on a t-stat it was on a heavily modded truck and I had two programmable e-fans. I ran a 185 t-stat and set the first fan to come on at 185 then the second at 195 in case the first one failed or I was at the drag strip so if the fan is kicking on around the t-stat temp you installed then that’s normal IMO. However, say it’s just idling in the garage and the fan comes on at 195 but keeps climbing until 210 or beyond then you could definitely have a fan issue. Easy thing to rule out at least.
 

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Discussion Starter #3
Thanks @MDK210 . I think that’s it. Pulled the shroud again tonight with the fan in it. Tried to hot wire it to see if it would run. Ran for about 10 seconds then quit. Couldn’t get it on again . So replacing. Will know more tomorrow but I’m optimistic !
 
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