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2015 Jeep Wrangler overheats at 70+ mph uphill

I have a 2015 JK sport with 33 inch tires and a winch on top of the bumper. I never have overheating issues until I am going above 70 and head uphill. The coolant levels are fine and it happens even when the outside temperature is below freezing. Where do I start looking for the problem?


Have you tried a new thermostat?

Not yet. I may give that a try. Thanks.

It should not be overheating in the conditions you are describing.
Has the cooling system been serviced? If this is the original six year old coolant, that is too long. Of course it is possible the temperature sending unit is malfunctioning. You could use an infrared thermometer to check for hot and cold spots in your radiator. At six years, should not be blocked with scale and rust, but possible.
At speeds over seventy MPH, what RPMs are you turning? Possibly gear ratio too high for those tires.

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That’s a really good point. I bought the jeep used and I really don’t know much about it’s past. Servicing the cooling system is a great idea. Re-gearing is on my to do list but it may now be moving to the top. Thanks!

Start looking here…

Blocking the radiator airflow, I’d guess.


That was my first guess, but replacing the thermostat is probably a good idea.

Check he odor/color of the transmission fluid.



How badly is it overheating? A little or a lot? And how steep are the grades?

I ask because I go to Colorado frequently and over the decades every car I’ve gone in (4 makes) has overheated to some degree while climbing grades. Not enough to hit the panic button, but it happens.

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It overheats to the point where it cuts back on power.

I did remove the winch today and it made no difference.

My next step is to service the cooling system and replace the thermostat.

I think ultimately that a re- gear may be needed.

Unless aftermarket gears were installed, you should not consider regearing.

OP has oversized tires on it.

The stock tire size would’ve been 225/75/R16 which works out to a diameter of about 29.3 inchs. The OP states that the Jeep now has 33 inch tires on it. The Sport model has a 3.21 axle ratio With the larger tires that effectively changes to a 2.94 axle ratio, which would be noticeable. a 3.55 ratio would put it back very close to stock.

Back when I had my Bronco I had a 33 inch tires on it, (stock was 235/75/R15, or about 29 inches). The factory gears were 3.55’s. With the larger tires it effectively became 3.21. a 4.10 gearset would put it effectively close to stock ( a little over actually), but I opted for 4.56 gears as I wanted better acceleration. With the 4.56 gears it was effectively a 4.10 ratio with the larger tires. Near perfect for what I wanted.

With that said I don’t think the gearing is the OP’s problem with the overheating.


Thank you for that info. My next step is to replace the thermostat and flush the system. If none of that works and gearing is not the problem then maybe a new radiator?

Is the fan even coming on . Normally at highway speed normal airflow is enough to keep it cool so the fan does not come on but if it is overheating on hills it sounds like the cooling fan is never coming on . I suppose it could be something like a partially clogged catalytic converter .

Good point. I’ll put that on my to do list.

How inaccurate is the speed sensor signal to the computer and how inaccurate is the speedometer? The transmission is likely electronically controlled and doing so with bad data.

We recalibrated for the larger tires. The speedometer is accurate as are the shift points. I don’t believe there is an issue in that department.

Radiator cap. This the classic symptoms of low system pressure. Don’t flush, just drain and refill. Flushing when not needed does more harm than good. A 2015 vehicle should not need a flush.

My kid had a 15’ wrangler and lives in Colorado. He could not drive up to pikes peak. Motor would die at 12k ft? I think he had it for 1 yr? Got rid of it. He tried to go up on 2 different occasions. Never mentioned overheating.

What brand/model front bumper does your Jeep have?