re: Jeep TJ 4.0 Engine overheating

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Don't thermostats typically go bad in the open position?

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Have had several go bad over the last 40 years, always stuck closed.

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Don't thermostats typically go bad in the open position?

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If you buy one with a failsafe. If not it's probably 80/20 of failing while closed/open.

Me personally OP, I'd buy a new cap and thermostat, and flush the system and check for leaks, replace any leaking hoses connections, and refill with new coolant and distilled water. It doesn't sound like a water pump, radiator, or fan clutch. Be sure to check up against the firewall where the heater core lines go in when checking for leaks. I chased a similar issue in my wife's Acadia that ended up being a plastic connection that had cracked and was weeping coming off the heater core and into a bypass hose.