Running around town or cruising down the highway to favorite wheeling spot and guess what - after an hour of fun and crawling your JK is overheating. The electric fan stays on constantly. Seems to mostly overheat at speeds below 10 mph. Sitting at idle, You checked the coolant at the fill and it appears to be full. Overflow is nearly empty. Could it be the pump? Does this sound all too familiar?
The coolant doesn't get enough time in the radiator to cool down so the whole system heats up eventually and the fan stays on trying to cool the fluid.
Another thing: Have you done anything to the grill openings? If so, what? Many of the aftermarket products reduce airflow to the radiator. Check the coolant reservoir to the minimum line when it's hot with the proper coolant (OAT certified for Chrysler vehicles).
If it drops too low when hot, then when cool it ends up sucking air into the coolant system. Get a bubble in the right spot and that can cause weird problems (overheating, heater not working right, etc), while your radiator looks full at the cap.
To check the thermostat, wait for the engine to be completely cold. Start it and feel the coolant hose on top. It should be cold until the temperature gets to some value where the thermostat triggers
Another thing: Have you done anything to the grill openings? If so, what? Many of the aftermarket products reduce airflow to the radiator.
Don't pend the money on the thermostat until you narrow it down to that. Though it's not an expensive part, it may not be needed and we have had vehicles that never needed a thermostat replacement and some that have. We suggest putting money towards a temperature gun which could be useful in troubleshooting this and many other issues. How long does it take from start up to over heat? Try to turn the heater on as it comes to temp...Does it blow hot? Does it noticeably (not sure if you have another source of reading or just the gauge on the dash) reduce the temperature?
If all else fails and all the checks are done it may be time a add a hood louver (aka Poison Spider style). There are numerous models and configurations out there - most require cutting an opening in the hood for install. But online videos with tips 'n tricks can take the experience how to learning curve out of the equation.
Travel safe - travel cool