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Discussion Starter #1
Ok guys I am new on this forum but not to cars/jeeps and other forums. I did the search but there is normally just people arguing/going off topic and not giving concrete answers. Here is my question for my 2016 JKUR 3.6:

At what temp does the thermostat open?
At what temp does the low speed fan kick on?
At what temp does the high speed fan kick on?

What is the top end of the safe operating temps on the 3.6 with everything being stock?

what is the top end of safe operating temps for the transmission (Auto)?

Is there an alarm/limp mode if the jeep starts to overheat?

Numbers please and thank you.
 

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Discussion Starter #4
Check out this video in the JK Tech section HERE

I think it will answer all of your questions and then some :)
Haha! Actually I watched the whole thing before I posted that. He does say 205-235F for operating range and under 200F for tranny, but he doesn't say anything about the other specific numbers. Mostly just common sense stuff - airflow and such. Plus he's talking about his LS and engines in jeep in general not a 3.6L Penta specifically.

thanks though!
 

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Discussion Starter #5
Agree, that is a great video for first time JK owners!

And, :welcome: to the Forum....
Thanks!

Below is my little jeep - 37's, 5.38's, some addons... Just trying to get the numbers so I know when to back off the throttle, especially when towing that camping trailer in the mountains.

 

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Gotcha :thumb:
Responses below in RED for what we've experienced with our '14 JKUR. We've towed with 4.10/32s, 4.10/37s and 4.88/37s. The '18 JK runs a little cooler.

At what temp does the thermostat open? Stock is 203, I've played around with 185 but it throws a code in cooler climates.
At what temp does the low speed fan kick on?
At what temp does the high speed fan kick on? It's been a while since I've read/discussed fan speeds, but it seems like it was around 225 for the high fan (depending on outside temps and other variables written into the computer

What is the top end of the safe operating temps on the 3.6 with everything being stock? Low 240s aren't uncommon for me in the heat and under load. Flat and minimal load I'll be in the teens-220s

what is the top end of safe operating temps for the transmission (Auto)? Not sure what top end is but I normally run mid 160's unless towing uphill or in a headwind, then I can reach mid 180's

Is there an alarm/limp mode if the jeep starts to overheat? Mine has given a check engine light under certain towing circumstances, like full throttle up a grade

Numbers please and thank you.
 

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Pentastar cooling system is complex it would chose the temp based on info provided by different sources/sensors.
below are the readings of mine 18JKU
At idle in P, AC off it would cycle between 208-226/228 when the fan kicks in.
With AC on will maintain roughly 208-210.
On the move it would be between 208-226. on flat roads below 212
However Ive seen 232 in stop/go traffic for short periods of time, fan kicked in at a higher speed then usually and dropped the temp back to 210.
Transmission is 165-180 most of the time.
 

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OP, you have some of these answers, already, but I'll fill in:

At what temp does the thermostat open? 203*, and they seem to open pretty quickly, just from monitoring temps. I haven't boiled one on the stove to visually test it
At what temp does the low speed fan kick on? 226*, with AC off, lower if the AC is on. This can be modified with HPTuners.
At what temp does the high speed fan kick on? These are PWM fans, so the duty cycle commanded increases with coolant temps, AC head pressure, etc. (The video is good for this info.)

What is the top end of the safe operating temps on the 3.6 with everything being stock? Ha! This is a good question. FCA would tell you below 250*. (See answer two questions down.) However, these are the same jokers who have a hard time keeping top ends in these things. My personal goal is low 230's under a hard load.

what is the top end of safe operating temps for the transmission (Auto)? Like most autos, low 200's - 2-teens, but you won't likely ever see that. The transmission cooler in these work great. Incidentally, the transmissions are thermostatically controlled to run at about 170*, so you won't see temps lower than that. Here's more info than you ever wanted to know about the NAG1/WA580 in the '12+ JKs.

Is there an alarm/limp mode if the jeep starts to overheat? Yes. The throttle will stop responding to input at 250* (on my '14, anyway), and I think they'll throw a code at 265*, IIRC. Hopefully you have enough sense to not let it get that hot.

Numbers please and thank you.
Mark
 

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Discussion Starter #10
Thank you everyone! Now I know what to look for and when be concerned. I'm not the kind of guy to just watch the dummy gauge so I'm thankful for the digital readout in the jeep.

Just a recap...

T-stat open at 203F
Fans are variable speed depending on conditions

Safe/normal engine operating is up to 240 for short times when under load. 250F is danger zone and throttle gone/limp mode.

Tranny is 210F danger zone
 
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