Heater core

[Lfarnz]

I have 2021 RAM Bighorn and have replaced the heater core twice in 2 years
Anyone else experiencing this issue?

 

[JoshsRam]

Same year and model and no, have not had this issue.

 

[Bass01]

We are having to replace the heater core in my 2013 ram 2500. Cost $2000 approx. Have talked to others replacing the core. Was a recall ever done?

 

[samsdad02]

just cleaned the core in my 14. Seems it happens a lot. I'm adding a bypass coolant filter.

 

[Yardbird]

Bringing up this thread. My 2018 is not putting out the heat it once did. The temperature reading on the gauge is the same, so it must be a clogged heater core.

I keep the air on recirculate, and with the A/C off, the heater air is not near as hot as it was last winter.

Dang...Was hoping the trucks with the Pentastar engine wasn't having this problem. Is it the OAT antifreeze causing this, or casting sand from the engine, or both?

I guess I will start with a backflush to see if that helps any. I don't drive it much, nor very far most of the time, but I do require good heat.

 

[RamDiver]

Bringing up this thread. My 2018 is not putting out the heat it once did. The temperature reading on the gauge is the same, so it must be a clogged heater core.

I keep the air on recirculate, and with the A/C off, the heater air is not near as hot as it was last winter.

Dang...Was hoping the trucks with the Pentastar engine wasn't having this problem. Is it the OAT antifreeze causing this, or casting sand from the engine, or both?

I guess I will start with a backflush to see if that helps any. I don't drive it much, nor very far most of the time, but I do require good heat.

Have you been able to confirm the coolant temperature and the temperature swing with proper thermostat action, monitoring the EVIC?

.

 

[Yardbird]

I watch the temperature on the EVIC. It's always between 194 and 203, according to how big of a hill I'm going up or down. That's where it's always ran.

The warmup time for the engine is the same as it's always been also. The only thing different is the temperature of the heat out of the vents.

I've never had to run the heat temperature all the way on high, but I do now just to get warm air.

 

[RamDiver]

There are many threads discussing the proper technique for back flushing the heater core and a few helpful YouTube videos too.

If back flushing isn't productive enough, some users have had very positive results using RMI-25. It's usually available at Amazon but not ATM.

https://www.amazon.com/gp/product/B004JVCJUU/ref=ox_sc_saved_image_6?smid=&psc=1

.

 

[Wild one]

Flushing A Heater Core

Come along with Eric O. at the SMA shop as we diagnose and repair this 2013 Ram 3500 Cummins that came in with a complaint of no heat out of the dash vents. ...

www.youtube.com

Heater Core Flush: Using CLR

In this video I show you the process I use to flush a heater core using CLR. I have done this many times in the past few years and it works extremely well. O...

www.youtube.com

 

[MaineRAM1968]

I have a 2021 2500 Tradesman and had the heater core replaced last December (2024) after having no heat on the driver's side. It was originally flushed, and was told there was a ton of "stuff" that came out by the dealership that maintains it. It fixed it for a week and then no heat on the driver's side again and little heat on the passenger side (not a good thing in Maine). They replaced the heater core, it worked, partway down the interstate, the heat was not keeping up. Took it back and they tweaked it a bit and it was working. Tried using the heat again a couple of weeks ago (in October 2025) and no heat again. It's back at the dealership and they told me the heater box that was replaced with the heater core was cracked. They said it was "redesigned" and has new parts. They also said that another truck was there having it's fourth replacement, same year - 2021, and they have had many in there for the same problem. RAM is aware of it but doesn't seem to be interested. Hoping the redesign and new parts will be a final fix. Doesn't even have 80,000 miles on it.

 

[Wild one]

I have a 2021 2500 Tradesman and had the heater core replaced last December (2024) after having no heat on the driver's side. It was originally flushed, and was told there was a ton of "stuff" that came out by the dealership that maintains it. It fixed it for a week and then no heat on the driver's side again and little heat on the passenger side (not a good thing in Maine). They replaced the heater core, it worked, partway down the interstate, the heat was not keeping up. Took it back and they tweaked it a bit and it was working. Tried using the heat again a couple of weeks ago (in October 2025) and no heat again. It's back at the dealership and they told me the heater box that was replaced with the heater core was cracked. They said it was "redesigned" and has new parts. They also said that another truck was there having it's fourth replacement, same year - 2021, and they have had many in there for the same problem. RAM is aware of it but doesn't seem to be interested. Hoping the redesign and new parts will be a final fix. Doesn't even have 80,000 miles on it.

You might want to look into adding a coolant filter inline with the heater hoses.
Go down to the Heavy Duty section in the 4th Gen section,and you'll find a few threads on heater core issues

Heavy Duty

A discussion for 2013+ 3500 and 2014+ 2500 Ram Trucks.

www.ramforum.com

 

[MaineRAM1968]

Thanks for the info on the coolant filter. Since I posted my original post, the heater core that was shipped to the dealership was cracked right out of the box. They finally received one that wasn't and replaced it. Heat was still sluggish on the driver's side while driving. Today, 12/5/25, I have zero heat yet again. It's a balmy 3 degrees today.

 

[jawzs2]

Sure sounds like there's something else going on that the dealer either hasn't found, or just isn't looking hard enough. That many heater cores in that short of time period is "unusual". Not saying impossible, but the skeptic in me says they're missing something. Have you talked to the service manager yet? If so and that hasn't gotten anywhere, talk to the general manager. See if you can make some progress

 

[Ramez]

They didn't even bother to flush the block??? mine had plenty of crud come out of the lower radiator hose after dumping the coolant, the air/water mix flush gun is used to push back into the block is vastly superior and the heat is like new again.

 

[mtofell]

Yeah, I had great success with a single flush after 11 years and a replacement engine (so two loads of sand, etc.). There's got to be more going than just a bit of sand. Maybe a lot of sand in the hoses, block, etc. Have they ever done an entire system flush? Or, just the core? It seems like they get the core clean and it just fills up again.

Getting some more specifics from them about if/what comes out each time would be helpful. The first time I did the flush there was a bit of a learning curve (I'm a few big steps below a lot of you here in terms of my mechanic skills) but I have the knowledge and things now and could pull it off in an hour or so. The biggest time-suck is removing/reinstalling the passenger wheel well liner. I'd just keep flushing each time the heat goes out and if that keeps restoring it then there's just a bunch of crap in there that needs to work itself out.

I'm not going the filter route yet since mine seems to be manageable but you might consider that. Sounds like they left a beach worth of sand in there!