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Place your bets- Why is this car overheating?

Posted on 4/20/26 at 6:07 pm
Posted by deeprig9
Unincorporated Ozora
Member since Sep 2012
75114 posts
Posted on 4/20/26 at 6:07 pm
Knowns-

-Fluid is topped off.
-Does not overheat when idling in driveway.
-Fan works.
-Overheats when driving.
-Cools down quickly when heater is turned on.
-Radiator installed in late 2024 (relatively new)

2015 Cherokee

This post was edited on 4/20/26 at 6:08 pm
Posted by deeprig9
Unincorporated Ozora
Member since Sep 2012
75114 posts
Posted on 4/20/26 at 6:09 pm to
Another known-

No check engine light.
Posted by W2NOMO
Member since Jul 2025
2253 posts
Posted on 4/20/26 at 6:10 pm to
Thermostat much?
Posted by HillabeeBaw
Hillabee Reservoir
Member since May 2023
3055 posts
Posted on 4/20/26 at 6:10 pm to
quote:

why is this over heating?



quote:

2015 Cherokee
Posted by TygerTyger
Houston
Member since Oct 2010
11048 posts
Posted on 4/20/26 at 6:11 pm to
Possibly a bad thermostat.
Posted by Loup
Ferriday
Member since Apr 2019
16770 posts
Posted on 4/20/26 at 6:11 pm to
Partially stuck thermostat, air in system, or collapsed hose.
Posted by deeprig9
Unincorporated Ozora
Member since Sep 2012
75114 posts
Posted on 4/20/26 at 6:11 pm to
quote:

Thermostat much?


If stuck closed, why would it not overheat at idle?

Why would it cool down when the heater is turned on? Does the thermostat not control the entire coolant flow?
Posted by deeprig9
Unincorporated Ozora
Member since Sep 2012
75114 posts
Posted on 4/20/26 at 6:12 pm to
All the AI's say a bad thermostat in this model throws check engine light codes.

I have no codes. No CE light.
Posted by Lonnie Utah
Utah!
Member since Jul 2012
34319 posts
Posted on 4/20/26 at 6:13 pm to
quote:

Thermostat much?


Posted by Kcrad
Diamondhead
Member since Nov 2010
66710 posts
Posted on 4/20/26 at 6:14 pm to
How's your water pump?
Posted by W2NOMO
Member since Jul 2025
2253 posts
Posted on 4/20/26 at 6:15 pm to
Low heat produced while idling. Bypasses the thermostat when heater is turned on. Acts as a mini radiator.
Posted by W2NOMO
Member since Jul 2025
2253 posts
Posted on 4/20/26 at 6:17 pm to
quote:

All the AI's say a bad thermostat in this model throws check engine light codes. I have no codes. No CE light.
I’ve changed many thermostats over the years. It’s the first and easiest to change. Nothing is certain but changing a thermostat is easier than water pump. Start with thermostat.
Posted by subMOA
Komatipoort
Member since Jan 2010
2018 posts
Posted on 4/20/26 at 6:18 pm to
Thermostat or water pump.

By turning the heater on, you’re adding a lot of excess cooling (engine cooling) capacity via the heater core now acting like a radiator and dumping that heat energy into your cabin.

Thermostat is cheap and easy.

What I said above about the water pump should be your next step- because of the pump is now at a lower flow state and needs the excess area in the cooling package to offset that.
Posted by WillieD
Lafayette/BR
Member since Apr 2014
3180 posts
Posted on 4/20/26 at 6:21 pm to
Ask your husband
Posted by deeprig9
Unincorporated Ozora
Member since Sep 2012
75114 posts
Posted on 4/20/26 at 6:21 pm to
I've changed thermostats in 1977, 1986, and 1999 models.

I agree, very simple.

Not simple in these newer vehicles.

Exhibit A-

This post was edited on 4/20/26 at 6:29 pm
Posted by SuperSaint
Sorting Out OT BS Since '2007'
Member since Sep 2007
149973 posts
Posted on 4/20/26 at 6:24 pm to
quote:

Why is this car overheating?

quote:

2015 Cherokee
because it’s past time to he put to pasture
Posted by Disco Ball
Denham Springs
Member since May 2025
1290 posts
Posted on 4/20/26 at 6:24 pm to
It's 11 years old
Thermostat
Failed coolant temp sensor or circuit including the relay
"Overheats when driving" is the fan coming on when driving? or only in the driveway?
"Cools down quickly when the heater is on" This sounds like a clogged and dirty radiator and it simply needs a "power flush" and an exterior radiator fin cleaning
Posted by Dog Tree
Member since Sep 2019
579 posts
Posted on 4/20/26 at 6:32 pm to
Have you confirmed it is actually overheating, rather than just looking at the temp gauge? Maybe a bad temp gauge?
Posted by RichJ
The Land of the CoonAss
Member since Nov 2016
5557 posts
Posted on 4/20/26 at 6:34 pm to
quote:

This sounds like a clogged and dirty radiator and it simply needs a "power flush" and an exterior radiator fin cleaning


I concur. I have a habit, every 5yrs, drain & flush cooling system, and replace coolant…
Posted by jaytothen
Member since Jan 2020
8648 posts
Posted on 4/20/26 at 6:39 pm to
quote:


By turning the heater on, you’re adding a lot of excess cooling (engine cooling) capacity via the heater core now acting like a radiator and dumping that heat energy into your cabin.


This guy knows how engines work
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