Good morning.

So I have a manual transmission 2013 Rubicon with 75K miles that I just bought in January used. Upon receiving the Jeep I noticed that the heater only blew hot air on the passenger side. Knowing that there is a casting sand issue I did a complete cooling system flush including reverse flow flushing the core which did the trick. While I was at it I figured I would replace the Thermostat since it was all apart for the flush anyway. I did this way back in February and everything has been running in ship shape.

Fast forward to the summer in NC and all of a sudden my needle on the temp gauge is sitting at 3/4 of the way while under moderate to low load (3,000 Rpms to maintain 50 mph). Once I get to a stop light the temps cool back down and the fan is running at overtime (Regardless of AC on, heat on, or everything off). I purchased the Flashcal and was monitoring the temps and thought that possibly the coolant temp sensor was reading incorrectly. I replaced the coolant temp sensor and rechecked. The flashcal and the gauge both read temps at idle of 213-230, but the thermometer on the heater inlet show around 195 at idle.

Also once the fan runs up it never shuts back down...it does cycle down to the lower speed, but it never stops (again regardless of heater on, AC on or none on). I am thinking that possibly the water pump is no longer pumping enough coolant through or it is time to upgrade to a more efficient performance radiator. The modifications to the jeep are 35" tires, 2.5" lift, Warn full length front and rear bumper with upgraded bumper mounted tire carrier. Warn 12,000 lbs winch which is sunk into the bumper to keep airflow open. I am about to re tear the cooling system apart to ensure I did not miss anything, all suggestions are welcome! Thanks everyone and hope your day is great!

 

3000rpm to do 50mph? What kind of gears do you have. Or are you not in 6th gear? Try getting the RPM down as the engine will run hotter with higher RPM as it is firing more times for a given speed. Also when you changed the Thermostat did you ensure it was the same temperature as the ECU needs to have a setting = to the actual t'stat temperature.
Long process for a short review but if you want to see if your water pump is working remove the t'stat put it back together and start the engine. Leave the rad cap off (do this from cold or warm) and have a friend rev the engine to 2000-2500 and observe the flow through the rad. You should see turbulence in the water and the level should drop a bit as water is circulating. If it is working, put the rad cap on, go for a drive to see if temps rise again with no thermostat. Won't hurt it for a short drive. Let us know what you find. The first test is for the pump function, the drive will determine if it is block/head related issue or radiator clogged if it overheats without a t'stat.

 

Its still the stock gears for Rubicon so 4.10 im assuming. I appreciate that, I will do this test this week and let you know wht I find, hopefully its a pump, radiator or just a bad new thermostat issue, would hate to be head / block related. Thanks!!!