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Clogged Heater core

I have a Dodge Dakota, that the heater core is clogged. I would replace it, but on this vehicle, you need to have the Air conditioning evacuated to remove the cooling core first. Poor design in my mind.

The cost of purging the system and then refilling it with refrigerant and testing it will add far too much to the repair costs, for this to be practicle.

Last fall I bought a small Drill driven pump and some extra hose. I flushed the core with CLR to remove any rust and corosion. Then reversed the direction of the pump. 20 minutes in each direction. The flushing seemed to help, but now that the cold weather has come, the heater air is still not warm enough.

I did test the CLR, on some Aluminum foil in a dish first, and it didn’t harm the foil, being soaked for 2 hours.

I would like to try this flushing again. Do any of you have any recomendations for chemicals that may clear the clog.

I’m thinking about trying some LimeAWay next. I tested that in a dish with aluminum foil and it didn’t harn it over a hour soak.

FYI; I also flushed it with Radiator flush then finished off with a Baking soda and water flush to neutralize any acid from the CLR.

Any ideas!!!

Are you sure it’s a clogged heater core? You’ve eliminated all other possibilities and have verified that the flow through the core is low? Some of the easier problems would be; coolant is not getting hot enough, blend door is not moving all the way over to the hot position, diverter (if equipped) is not operating properly, etc. The heater inlet hose should be roasting hot when felt with your hand. Is it?

There shouldn’t be any mineral clogs if you’ve used distilled water in the system and maintained the coolant. CLR works on these minerals and if you’ve kept the coolant fresh, there shouldn’t be any accumulation of rust either. I doubt those chemicals will do much. They’re not strong enough to dissolve a plug when the flow is minimal unless given a really, really long time to work. I think any caustic solution strong enough to dissolve a clog in those tiny passages will likely be strong enough to also damage the metal of the core.

have you checked the actual temperature of the coolant when the engine has been run? if the air is coming out of the vents too cool, and the radiator is HOT then there is a core problem, but… if the radiator is cool as well, then the thermostat may be broken.

the diverter valve mentioned by TT is suspect if the temp is ok for a while, then if you change the temp selection and it goes haywire. have you had a temp problem in the summer with the AC? like, if you had the ac on, and change the temp the ac won’t cool? there is no diverter valve on this truck.

you mention flushing the heater core. if you have been able to flush it, then it isn’t clogged!!!

how did you flush it? by removing the hoses inside the engine comp at the fire wall?. my money is on the thermostat or the water pump is failing.

how long has the is been happening? what year truck?

You should use a chemical flush that is made for automotive use and follow the directions carefully. You can find them at an auto parts store. I don’t recommend using products that are not made specifically for that purpose. I also recommend buying and installing a flush and fill kit to make sure you get all the chemicals out after they have done their job.

1994 Dakota and the flushing was done in April of last year. It seemed much warmer after the flushing, but now that the weather is in the 20s it surely is more noticable.

I’ve never cut a core apart but I presume the fluid is flowing into the top of the core’s tank and right back out the outlet tube instead of flowing through the core tubes or only flowing through very few of the tubes… Is that possible???

The temp in the Radiator (new this summer) is at 174 degrees. With a new thermostat.
I think that was a 185 degree thermostat and the 174 would be normal with it just sitting and the fan helping cool the fluid.

I checked the blend door also and seems to be working properly.

when flushing I connected the drill pump hoses to the core inlet and outlat and the reversed the flow too.

THe inlet hose to the core is nice cand hot, but the outlet hose is no where warm enough.

I did first use a radiator flush product, but it didn’t help increase the temp at the heater.
Thats why I used the CLR. When I was finished, I filled the core with Baking soda and water solution to neutralize any caustic chemicals. Then, because the hoses were off it was easier to just hook the garden hose to it and run that for 10 minutes for a good flush, before hooking the heater hoses back up.
It did seem to help, but must have plugged back up again during summer.
I may just try the Limeaway and be sure to flush it real well along with the baking soda flush. Either way, if it doesn’t work, My mechanic is only 6 miles down the road.

Are you sure you got all the chemical flush and baking soda out of the whole system? I have seen problems like this persist because someone didn’t adequately rinse the system out. I would add the flush and fill kit to be sure the whole system gets both flushed and rinsed. This way you don’t need to disconnect any hoses and you can be sure you flush the whole system, not just the heater core. After all, you might have blockage somewhere else in the system that is causing your problem.

I’ve never cut a core apart but I presume the fluid is flowing into the top of the core’s tank and right back out the outlet tube instead of flowing through the core tubes or only flowing through very few of the tubes… Is that possible???

Not on any of the heater cores I have seen. The only way to get from the inlet “tank” to the outlet “tank” is through the core capillaries. It’s a smaller version of the primary radiator for your engine. If you have good flow from inlet to outlet, it has to be passing through the core.

That was my purpose in hooking up the garden hose to the system. The core, with the chemicals was never hooked to the whole cooling system until after a good flush. I even reversed the hose so I’d backflush anything out, before reconnecting the core to the system.
I wouldn’t want to use a “flush kit” with these chemicals…knowing some of it would migrate towards the engine itself.
Hooking up to a flush kid DOES NOT close the passage to the engine itself.
Unless you’d crimp the hoses toward the engine with a visegrips or something.

Besides the radiator is new, the coolant is new and clean as a whistle. Why contaminate the radiator and coolant with whatever you disolve. I’d rather disolve whatever is there and not allow all the disolved crud into the whole system.

My point was that there could be blockage in another part of the cooling system other than the heater core that is causing your problem. Besides, if you follow the directions, the chemical flush should be safe for the whole cooling system.

Unless you are 100% sure the blockage is in the heater core, you might be barking up the wrong tree. Personally, I would not make that assumption, even if the coolant is new and clean. Otherwise, you might discover you have been ignoring the crud that is already in another part of the cooling system.

But hey, you seem to know what you are doing, so keep doing it and maybe you will get different results next time.

Well, I knew that I was taking a chance. The heater core could be worn enough, that the chemicals would cause a leak and I’d have to replace it antway.

Two days ago I flushed it with the pump on a drill. I used 1 pint of lime away mixed with 5 pints of water to dilute the solution a bit. One hose that went to the pump was the clear kind, so I could see that the solution was in fact flowing.

I filled the hose with a funnel until the solution was comming out the other hose. Then I knew it was full. I connected the lines to the pump and ran it for 1 minute, pause for 1 minute. I did this over and over for about 15 minutes.
Then with a funnel flushed the whole thing with clear water. Then flushed with a baking soda and water solution leaving it sit in the core for a few minutes.

Flushed the whole area with a baking soda solution also, to be sure no caustic chemical spilled on anything.

Hooked it all up and I now have great heat, with no leaks.

It worked great, but I knew I was taking the chance that I’d creat a leak…


I don’t want to be Captain Obvious here and don’t wish to insult you . . but this could very well be air in the system. It happens to the best of us, and air is sometimes hard to remove given the unique designs of some cooling systems, designed partly to “fit” within the vehicle, and not necessarily to work without “glitches”. My first idea would be to “burp” the air out of the system. After that I’d find the actual valve which controls the coolant flow into the core and lubricate it well, work it by hand a few times to make certain that it is opening & closing completely. I’ll try to think of anything else . . but your CLR idea was a good one and you seem to know what you’re doing by the method you used. Rocketman

Wooooo–hoooo! After all else failed, THIS METHOD WORKED! I tried flushing and filling, changing my t-stat, checking the blendor actuator, trying to flush out my clogged heater core, nothing worked. So thank you very much, I now have hot air coming out of my vents !