Thermostat showing hot, radiator fan high, low heat in car. - Jeep Wrangler Forum
Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > JK Jeep Wrangler Forum > JK Tech Forum

Join Wrangler Forum Today

Like Tree2Likes
  • 2 Post By Bob Sanders
Thread Tools

Please support our sponsors and let them know you heard about them on
Old 10-10-2019, 12:03 PM
Thread Starter
Join Date: Mar 2016
Posts: 3
Thermostat showing hot, radiator fan high, low heat in car.

Little background:
I have 2012 JK 2 door. I live in NY, so cold winter and hot summers. Last winter the interior heat stopped working. Tried a coolant flush, checked the blend door actuator, still couldn't fix it. I felt like the the coolant was getting clogged or low flow somewhere. Brought it to dealership and said it wasn't that the whole heating core need to be replaced. Didn't give a crap what I thought. Paid $2500, heating worked for the rest of winter.

For the past couple weeks of summer the thermostat is showing very warm. 3/4 of the way to Hot, instead of usual 1/2. It bounces pretty wildly between these 2 points, like a couple of seconds to go from 1/2 to 3/4. This is during normal suburban traffic. And whether at a traffic light, or driving the thermostat is still slowing bouncing all over the place. Radiator fan roars during all this. I recently went in to for a recall to the dealership and mentioned to them, they said they were only able to replicate it slightly and said it's just a little warm and not to worry...wth.
Busy with work so have just been dealing with it for a month. Now it's getting colder again outside so i turned on the interior heat. The heat does not work now. Just the same as 9 months ago.
Surely this is all related.

I feel like the the engine is getting warm but the rest of the coolant path is semi-clogged or getting poor circulation somewhere. The car is getting no heat from the heater core and when I get out of the car and move to the front while the roaring radiator fan is blowing cold air out at me and not warm in the slightest.

Any thoughts?

thegrim is offline   Quote
Old 10-10-2019, 12:35 PM   #2
ssinga's Avatar
Join Date: May 2014
Location: Alabama
Posts: 1,307
sounds like it could be casting sand. have them fix it again then add a filter to the coolant system.

My JKUS Build 2012 JKU Sahara #777,820
ssinga is offline   Quote
Old 10-10-2019, 12:51 PM   #3
Supporting Member

5-Year WF Supporting Member
TagBannedAgain's Avatar
Join Date: Mar 2018
Location: S.E. Michigan
Posts: 196
I had the exact same problem. I replaced the heater core and it still is getting sand in it, it's the low point in the system.

Temp jumping around sounds like there is air trapped.

As Ssinga said, your heater core is probably got more sand in it. I have had mine flushed twice in the last 2 months (5 times this year since Feb.). The first time no heat , drove it for a month flushed again & now I have about 120°F @ the vents. Still not as hot as it should be.

Skip the dealer and go to a reputable radiator shop to have it flushed if your not doing it yourself. Try to find one that has the machine that puts a vacuum on the system to get as much air out as possible.
TagBannedAgain is offline   Quote
Sponsored Links
Old 10-10-2019, 01:22 PM   #4
Bob Sanders's Avatar
Join Date: May 2017
Location: Winnipeg, Canada
Posts: 4,266
I would suspect air in the system and work on that idea before jumping to more serious conclusions. Indeed temp jumping around and cooler air from the rad is an indication of air.

Was your overflow tank empty for any period of time? If left empty for a good period of time you will will start sucking air onto the system. The overflow must stay between the min/max marks at all times. A lot of people don't really understand this and they let the tank go dry.

It should be noted that a leak in the system will also suck air
Old Dogger and Wrangleur like this.
Bob Sanders is online now   Quote

heater core , hot engine , radiator fan , thermostat

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -5. The time now is 03:10 PM.

Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.1
User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.

Jeep®, Wrangler, Liberty, Wagoneer, Cherokee, Gladiator, Mopar and Grand Cherokee are copyrighted and trademarked to FCA US LLC. is not in any way associated with FCA US LLC.