Originally Posted by Solidus106
Bump with an engine/drivetrain description?
Some models have temperature sensors that are crap, as well as oil pressure sensors.
Thermostat installed backwards or with gasket material interfering with closure?
What radiator do you have? Factory or aftermarket?
Coolant changed per schedule, or allowed to stay in there and crud up?
Non-distilled mineral heavy water ever used to thin pure antifreeze or always use premix?
Failure to burp air from the system on replacement?
Any spongy hoses?
Water pump OK?
Cooling fan OK?
Can you see coolant moving in the radiator once it hits thermostat temp? [leave the cap off as it heats up]
The 4.0 six runs cool at temps in the 130 range with cooling system in halfway decent condition. You have a bit of extra heat load from the Houston levels of humidity, but 80 degrees shouldn't be at all an issue.