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I have replaced everything short of the water pump. Truck runs at just over 210 typically. Unless it goes over 70 MPH. I have flushed the system, replaced the t-stat twice, replaced the radiator and both hoses, cleaned the radiator with hose from front to back and back to front.
It will jump up to the bottom of the red, until I back off the throttle for a few minutes, then it will drop back down. No leaks, no overheating, heater works. I also bought a new fan clutch (not that it was logical because of the highway speed, just because I've tried everything else) but that did nothing. The Jeep stays right at I guess about 220 during normal city driving, and as long as I keep it under 70 MPH it will stay the same on the highway as well. it does have aftermarket wheels and the tires are slightly larger than stock, but I didn't have this issue when I got the truck (with the same wheels/tires).

I'm losing hair over this because it seems to not make any sense. Could it be a sensor? it seems the temp sense is working fine..

HELP!
Thanks in advance.
 

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Rent a pressure tester from chinazone...while you're there buy a new cap if you haven't already. If your system doesn't hold pressure the coolant will boil making the temp unstable to say the least. I think a 50/50 mix has a boiling temp of 22x*...don't remember the exact number. With 18 lbs it's raised to 270+.

It could also be the pump but if it's not showing any signs that's probably not it.
 

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if this is a 4.0l you've got a cracked head - google it. Huge problem on 2000- 2002 4.o engines. I think its the infamous 0331 issue
 

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Does the bottom hose have the full length wire support in it. It needs the support because it is the suction side of the system. If you can squeeze the hose shut anywhere then it might be collapsing when it speeds up. and when you slow down it opens back up. Just give it a squeeze to make sure. Cracked heads leak water into the oil. Pull the dipstick and look for green milkshake. If its clean oil then it is not the cracked head problem. Not all the trucks got cracks.
 

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check your drain too, i know mine was just a tad bit open just barely dripping but my radiator kept getting airlocked, i would pop my cap off while cool the fluid level would be really low, cranked that drain all the way closed and not a prob since, it stays right below 210 now
 
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