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Discussion Starter #1
I have regeared my JKUS from 3.73 to 4.56, running 315/70/17 Duratracs.

Even before regearing my jeep would consistently run up to 226-228 and then can would kick in and cool it off fast. Also it was not as hot outside at that time. I regeared in early May and took 2 long distance trips and noticed that now, when I am accelerating to highway speeds off the ramp, or have to climb a hill at highway speed, my jeep always goes to 230-235 range until I am done with climb or accelelaration.

when cruising at highway speeds, going 70-75 MPH (2700-2800 RPM with 4.56) on a cool day, I see 222-224, when it's 85 degrees and up day, it's 226-228 constantly.

as soon as I give it a bit of acceleration to 80-85 mph or hit a hill, it climbs to 230-235 again.

it does not go above 224-226 when I am in the city stop and go traffic, but the fan is ALWAYS ON. Transmission temperatures are always in 161-163 range.

Should I take it in to have a cooling system checked or is it more or less normal behavior, amplified by higher RPM after gear swap and I just should keep my speeds in check?
 

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2700-2800 RPMs at 75 MPH sounds pretty high. That sounds like it isn't going into OD.
 

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Discussion Starter #3
it looks about right for 4.56 gears based on few posts. I did use flashcal to adjust for gear ratio and tire size.
 

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Is it an Automatic or standard? I don't have a way to tell exact tempature but in theory a regear would cause less strain allowing the engine to be cooler. Is the radiator full? How much of the grill are you blocking? I have angry bird grill, 7'' lights and a winch and I never go above the middle mark on temp. Just re-geared to 4.88 from 3.21
 

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Discussion Starter #5
Is it an Automatic or standard? I don't have a way to tell exact tempature but in theory a regear would cause less strain allowing the engine to be cooler. Is the radiator full? How much of the grill are you blocking? I have angry bird grill, 7'' lights and a winch and I never go above the middle mark on temp. Just re-geared to 4.88 from 3.21
it's an Auto 2015. radiator is full, I even burped it once, using the funnel and added some Mopar OAT coolant that I bought at the dealer. expansion coolant tank has enough coolant in it. I do have a winch and a light bar in front of my grill, also, I have mesh screen DIY mod. up to 226 is the middle mark, 228 is just a bit over, and 235 is half way between 1/2 and 3/4 marks
 

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I'll run mine home today @ 80-85 and i'll see if the temp increases, I know for a fact my fan doesn't run constantly. I've left it under my carport running and it'll kick on but will cycle off longer then it is on. I always let it finish cooling cycles before shutting off, Motorcycles gave me that habit. It might not be moving air through the radiator as much as it wants to so that would explain the fan. You say it cools fast too in my experience sticky thermostats cause that, meaning the coolant is staying in the radiator or engine longer then typical. Also this sounds like a minor problem so don't sweat it too much. Thermostats are real cheap and an easy fix, housing I believe is plastic which is easy to break so if you go that route be careful. Your not really out of the normal range for temp but it seems a bit on the high side.
 

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Actually a sticky thermostat would cause the fan to run more also...
 

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Higher RPM = More Heat

You are working your engine harder with the increased RPM so it will generate more heat.

You may want to look into more cooling, like hood vents, a better electric fan or a bigger rad.
 

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Higher RPMs do equal more heat it he isn't revving to the moon he's around where a rubi with 4.10s and a auto would be. There's another issue here. Plenty of people have ran that combo.
 

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Higher RPM = More Heat

You are working your engine harder with the increased RPM so it will generate more heat.

You may want to look into more cooling, like hood vents, a better electric fan or a bigger rad.
kinda off topic here. but that depends if its hilly or not. if hes going up a hill, higher RPM's usually mean less work on the engine. Its a lot harder for an engine to stay at low rpm while going up a hill than high rpms. think of a bicycle in low gears vs high gears. you may be spinning faster, but its easier to do
 

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Discussion Starter #11
it heats up fastest when I accelerate or go uphill
 

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it's an Auto 2015. radiator is full, I even burped it once, using the funnel and added some Mopar OAT coolant that I bought at the dealer. expansion coolant tank has enough coolant in it. I do have a winch and a light bar in front of my grill, also, I have mesh screen DIY mod. up to 226 is the middle mark, 228 is just a bit over, and 235 is half way between 1/2 and 3/4 marks
One thing I was told that if you have green anti-freeze never add red and vice versa, the chemicals in the two can cancel each other out and cause problems, mostly rust issues but others issues as well. Probably not your problem though.
 

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Discussion Starter #13
^^^^
yes, I was very aware of this issue. that's why I went to dealership to get compatible coolant - OAT vs HOAT
 

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Discussion Starter #14
anyway, I just dropped the jeep at the dealer, lets see what they say. I have a warranty and will let them deal with it. Probably will get a new thermostat as a first step
 

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Higher RPMs do equal more heat it he isn't revving to the moon he's around where a rubi with 4.10s and a auto would be. There's another issue here. Plenty of people have ran that combo.
I am not sure that he does have an issue other than the mods he has made to his Jeep. He is not overheating but his mods will build more heat. Higher RPM, more rolling resistance due to larger tires, and with the new bumpers I can only assume his front air dam is removed. Since his Jeep is a 2015 I doubt his themostat is a problem since his Jeep was not running as hot before his mods. He may get lucky and need a PCM update. I know my 2013 had one concerning the electric fan but reading what was posted I can only guess that the mods to the Jeep are making it run a little hotter and that more cooling of some kind might not be a bad idea.
 

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Discussion Starter #16
I am OK with that, as long as the ruling is out that my cooling system has no problems, I will start looking at upgrade. but I see plenty of jeeps set up like mine run around with no issue
 

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Yea I have a 2012 with more air restriction in the front and I live in hill country texas so 100* days and 4.88 putting my RPM @ 3000 when around or just under 80MPH. I haven't noticed my temp gauge ever being over 226* (thanks to the OP I know that's the middle mark on the gauge) But every jeep is different and like you said he's not really overheating or showing signs of failure. I'll confirm my temp on the way home tonight, i'll run it hard and see if I cant get the temp up.
 

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it's an Auto 2015. radiator is full, I even burped it once, using the funnel and added some Mopar OAT coolant that I bought at the dealer. expansion coolant tank has enough coolant in it. I do have a winch and a light bar in front of my grill, also, I have mesh screen DIY mod. up to 226 is the middle mark, 228 is just a bit over, and 235 is half way between 1/2 and 3/4 marks
I added a winch and a cover for it. Coming home yesterday I noticed the temp up around 230 or so. Took the winch cover off and it cooled down by about 10 degrees. Lights, winches, covers, etc. all add up to less airflow. My theory anyway...never ran that warm before the winch.
 

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2011 JKUR stock 4.10 gears 3.5 lift 37" big heavy bumpers winch 105 degrees 100 mile road trip up/downs hills 50-75mph ac blowing on hi, never above half way on temp....

check your thermostat
 

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2011 JKUR stock 4.10 gears 3.5 lift 37" big heavy bumpers winch 105 degrees 100 mile road trip up/downs hills 50-75mph ac blowing on hi, never above half way on temp....

check your thermostat
2011? Is that a 3.8? The 3.6's will run warmer, I believe. Normal temps are from 200 to 226 on the 3.6, but they will run a bit warmer with a load on. I would say the OP's conditions are completely normal...nothing to worry about.
 
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