HogHoden

I've searched, talked to local jeep owners, etc. and have not been able to identify a cause, any help would be appreciated.

Symptoms:
25% of the time, heater works fine
75% of the time, luke warm/cold air blows from all vents when idling - engine warm. When the gas is pressed, the air changes to hot. Let off the gas, back to cold air.

2012 JKUR with about 70,000 miles. Coolant was drained and replaced last year, but no flush.

Any body have a clue what could be going on here?

Mark Doiron

You may have a bubble in your coolant system. If that bubble gets lodged in the heater core, it's less efficient. Check out a YouTube video or two on how to burp a cooling system, then do that. Have some coolant handy so you can top it off once done. Be certain to get the right coolant for your vehicle. My recommendation: Steer clear of universal coolants and buy direct from Jeep dealer. If you aren't sure what was used when it was last changed, check with whoever did it and use that and hope for the best. Bottom line: It's no longer safe for your engine to mix coolant types, and you'll get longer life from the coolant manufactured to Chrysler's standards.

Rednroll

You can refer to my thread below, which just happens to be 15 posts away from yours on your endless search.
https://www.jk-forum.com/forums/stoc...roblem-339178/

The 1st post lists the top 13 causes of heater related problems. Based on your symptoms, you're likely looking at #2, #7, or #13. Most likely #2 as Mark described.

The best way to burb the system is to raise the front of you JK on the side of the radiator cap so the radiator cap is the highest point......Air always travels to the highest elevated point. Then with your JK running, start filling into the radiator little by little while squeezing the top radiator hose to get all the air out of the system.

newcomb

Thanks for the link Rednroll! I have the exact same issue as the OP but hadn't started my search through the forum for a fix just yet. Made my life a little easier.

appst8design

I had the same issue with my 08. I have a known coolant leak I've been putting off fixing. Every time it gets low the heater stops working while at idle. Throw some coolant in there and see if it works.

cabmak4life78

Yep these folks are on the right track with the system needing to be burped. I had the same symptoms about two weeks ago after changing upper/lower intake gaskets. After the burp everything has been running just fine for the last 1500 miles.

jscaccia

My problem is that the only way the heat works is when its on the hottest level on the thermostat. When I move it any bit cooler it just goes to cold. Dealer told me to replace heater core.... I don't have an odor, no fogging of the windshield, and it does get warm when you put the thermostat all the way to hot. I took the car to another mechanic and he said the heater core looks fine. Not sure what the issue can be. Any suggestions?

resharp001

Is this possibly a blend door issue? The fact that it's affected by simply changing the setting even a little off the hottest level would have me searching in that direction.

Rednroll

Yes, sounds like a blend door issue. My guess would be is that some of the gears have stripped on the blend door actuator assembly. Probably should do the telescopic camera to confirm full movement of the blend door as I did in my diagnostic discussion. That blend door repair looks like a major pain, but some with small hands and lots of patients have done it without removing the entire dash. I have neither, so I was really thankful my blend door wasn't the problem.

HogHoden

Late reply, tried everything suggested with no resolution, then summer came. Thanks to all for the suggestions. I'm hoping I finally have it solved. I replaced oil filter housing ( Mopar 5184294AR) and the thermostat and overflow bottle. A couple of weeks ago, I had the overflow hose blow off of the radiator filler neck, and the end of the hose permanently expanded enough that it wouldn't fit tight any longer (even with a clamp added). Both the oil filter housing and thermostat had coolant leaks small enough (or only under pressure) that I never saw any coolant, it was either evaporating or blowing off in the wind. With both of those replaced last week, I've consistently had heat as normal. Haven't put a thermometer in the vents yet, but feels scorching hot again like it should. This year the leaks must have gotten worse, as I did notice the coolant disappearing and was having to refill. Apparently the coolant leak from the oil filter housing is common, usually not big enough to see any visual evidence, as it leaks onto the top of the engine and evaporates before it can run down.