jadmt thats good to know, made me curious as to why it would be like that and found a service manual for the trans Just read into this trans a bit more, turns out they use the temp sensor as well to determine if park or neutral is selected for starting.

"The TCM monitors a contact switch wired in series with the ATF temperature sensor to determine Park and Neutral positions. The contact switch is open in Park and Neutral. The TCM senses transmission temperature as high (switch supply voltage), confirming switch status as open. The TCM then broadcasts a message over the CAN bus to confirm switch status. The engine controller receives this information and allows operation of the starter circuit.

 

Based on the post above, it sounds like the TCM is reading full voltage at the transmission temperature sensor rather than coolant temperature.

 

Last weekend I took my 13 JKU Manual to the Ocala national forest. first 2 hours was great never even had to put into 4WD. Then 1st gear crawling up a slight slope in sugar sand my check engine light came on and shortly after that my temp gauge skyrocketed. I immediately shut her off and let her cool down for a bit. could hear the fluid boiling from somewhere in the engine bay possibly the block but I didn't have enough time to investigate. after and hour or so I found the nearest auto parts store and hooked up the OBD to find out the check engine light. It read bad cooling fan circuit. however on highway speeds and regular daily driving not a single problem, and the check engine light went away without me having to clear it. I also looked in the radiator and it was kinda brownish fluid. Thinking it was the Tstat or a bad fan I checked all of the above and the fan came on when the engine was at temp as it should and the fluid was being cycled thru. any help or suggestions to fix this issue would be greatly appreciated.

 

There is a wire at the battery that if it's loose, can cause a fan to not work properly. I'd check that first.

 

I am currently trying to understand how my 2015 JKU ran half temp or less for 2 years and now after replacing my thermostat it runs just above half way point or higher at 45-55 mph and when I accelerate to highway speeds it goes up past the 3/4 mark and from my understanding that's like 250+ !! I'm pretty frustrated. Changed thermostat but didn't use OEM.. could be problem but I'm not sure yet. Just changed ECT sensor to see if maybe that was giving a faulty signal some how..but no change after replacing. I have also NEVER had my fan kick on for more then a minute before and that's sitting at drive through. Now the fan runs constantly and is always in it's high speed mode. Somebody hadta have had this issue before so if any of you read this and know how to correct this please share because I'm very sad about it and tired of dumping money into the wrong things. I do plan on trying the OEM thermostat as a last resort. It's 98 bucks compared to the 26 dollar one I put in it.

Not sure the accuracy of this image but seems legit

 

I can only speak for myself, but this is one of those parts I'd stick with Mopar. You should find that ~$65 and not almost $100.



I have a '13 myself. I would say this old picture is not accurate to what I've observed on my temp gauge. I monitor my temps pretty close via my tuner and I've seen temps as high as 250° on mine in the past. From what I recall, that was pretty dang close to the red H line on mine. I'd say 240° is solidly at, maybe even a little over, that 3/4 hash line. I'm just going by memory so I could be wrong. My normal normal temp via the gauge is over the halfway mark. I don't trust that gauge much more than a quick visual. I'd certainly rely more on an actual number provided by the jeep's computer be that from dash if you have it, or some unit that is plugged into the OBDII port..

 

were you able to get this resolved? I have the same problem and still haven’t been able to figure it out after dumping tons of money at it

 

At the risk of repitition - my neighbour is a good mechanic (young and good) and his wife's GC Pentastar had heating issues so he installed a Hemi Rad in there (GC's came with a hemi) and it runs at about 200-205 on the hottest days here at 95F. He says it pulls a lot better with the cooler operationand wants to take it down to 195 but need to buy credits to use my HPT to alter the engine temp setting in the program. Cooler is better and looks like that Mopar bigger rad did the job. He did the chains, phasers and cams when he bought it as he beat up the previous owner on price as it was not in good shape.

 

I REALLY appreciate your response because I've been thinking something went horribly wrong with my Black Beauty!! Yes, I regularly run hot too and I'd also like to know how the OP got theirs to run so cool 😎

 

Long story short I typed a long reply only for it to not post, but the gist of it is that our T stats open at low 200’s and should be fully open about 220-225 or so, if we are seeing temps above 225 or so it’s because the heat we are making exceeds the cooling systems capacity to shed it. I believe it’s because we don’t have exh manifolds and therefore we are dumping much more heat into the cooling system than normal.

If I’m correct then the only real fix is a bigger radiator AKA increase the size of the cooling system.

I’m very new to this engine having just bought my new to me used Jeep but if we are dumping that much heat into the heads as we have overhead cams there are or will be I think valve train issues and if we don’t run good oil and are diligent about changing it we may get both sludging and maybe coking in the heads, coking less likely, but I’m going to shorten my oil change interval over the recommendation by a lot myself.