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How to test a heater core

Curt Chambers

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I've currently got my heater box (73 Charger) apart and want to make sure the heater core is solid before putting it all back together.

I can inspect for obvious damage and rust. But is there a way to check for pinhole leaks that only show up under pressure? I do have a radiator pressure tester but not sure how I could adapt it for this use.

Thanks
 
You can seal/cap one side and pressurize the other. I used 5/8 hose and a few fittings with a air schrader valve. Max pressure 16 psi like a rad cap.I usually go no more than 10 psi.You can fill with water or just use air.I found the schrader valve at a hardware store.
 
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Put it in the car and see if the floor gets wet like the rest of us!!!!!!! Just messing. It always seems every car I hook the heater hoses to it leaked lmao!

:thumbsup::rofl:
 
I put my new heater core for the El Camino in a bucket of water and used the compressed air method described above.

I think every new core should be tested prior to installation given how hard it is to change and the damage a leak will cause.
 
If you don't have a Mity-Vac hand type vacuum pump in your tool box, you might consider getting one. Testing a Core is one of many tests done with a vacuum pump.
Get a couple neoprene test tube stoppers of the proper diameter. One should have a hole in it. Plug one nipple with the solid stopper and put vacuum to the other and see how long it holds vacuum.
A free preliminary test would be to plug one nipple with your thumb, suck on the other all the vacuum you can muster and let your tongue be the second plug. It will leak down right away if it does.
 
Thanks for the good suggestions.

Actually I do have a vac pump, but it always shows a slow leakdown so it's not very reliable.

I'll try the pressure test. But I'm not really visualizing how to attach the schrader valve to the heater core.
 
5/8'' Rubber heater hose. The hardware store(or RV store) has a plastic plug/ schrader valve that uses a air chuck for RV's to blow out water lines for winter storage. male water hose fitting.You can use a water hose male end fitted to the heater hose with anything/fitting/hose clamp to connect to the heater hose.
The hardware store had a schrader valve that had a 1/8 pipe thread on it and I made a adapter fitting to attach to the hose end.
 
As suggested, I was able to find everything at the local hardware store. Got everything hooked up. Dunked it is a tub of water and started to pressurize. A geyser of air bubbles immediately erupted from somewhere in the middle. I never even got 3 lbs of air pressure in there. So I need a new core. No big deal. CI has them for $100.

Next question. Can I test the A/C evaporator in the same manner?
 
You may want to research before you buy an after market heater core (they don’t always fit right). If your current heater core is original I would have it repaired (just my opinion). I used Glen-Ray for repairs and was very happy with the result. I would do some research prior to buying.
 
You may want to research before you buy an after market heater core (they don’t always fit right). If your current heater core is original I would have it repaired (just my opinion). I used Glen-Ray for repairs and was very happy with the result. I would do some research prior to buying.

I would send mine to get rebuilt if you want it to fit right in the case...
 
I've checked locally and no one repairs them anymore.

I really hate sending stuff out into the black hole to be repaired. I hear too many horror stories of people waiting a year or more to get stuff back.

HD539, did you purchase a heater core from CI that didn't fit? I'm trying to pin down exactly what these fitment issues are.

Thanks.
 
As suggested, I was able to find everything at the local hardware store. Got everything hooked up. Dunked it is a tub of water and started to pressurize. A geyser of air bubbles immediately erupted from somewhere in the middle. I never even got 3 lbs of air pressure in there. So I need a new core. No big deal. CI has them for $100.

Next question. Can I test the A/C evaporator in the same manner?
If you expose the evaporator to water during the test, make sure to put a vacuum on it to boil off any moisture in it before sealing it up prior to installation.
 
DO NOT BUY AN AFTERMARKET HEATER CORE!!! Yes I meant to have caps on.... I tried four different suppliers before having my original re-cored...
 
No, I’ve purchased plenty from CI (not a heater core), but was advised that all to often the aftermarket heater cores often don’t fit correctly. There are lots of examples I read about where the tubes were to short to penetrate the firewall or the heater core didn’t fit in the box correctly. I found that Glen-Ray turned it around rather quickly and did an outstanding job. Certainly your call, just thought you should beware and do a little research. Best of luck.
 
Update: I couldn't find anyone locally to work on this. So I took a chance and ordered a replacement heater core from Rock Auto. They must be getting better with their repros because the one that arrived is an exact replica of the one I took out. It fit perfectly. Maybe they are still missing the mark for other generations, but they nailed the 71-74 B-body.

Anyway, just an FYI for anyone doing the same project.
 
An easy way to air check a heater core is to get a cheap road bike innertube. Cut it about 4" on both sides of the Schrader valve and clamp the open ends to the heater hose fittings. Can do the same thing with a radiator using a mou tain bike tube.
 
Update: I couldn't find anyone locally to work on this. So I took a chance and ordered a replacement heater core from Rock Auto. They must be getting better with their repros because the one that arrived is an exact replica of the one I took out. It fit perfectly. Maybe they are still missing the mark for other generations, but they nailed the 71-74 B-body.

Anyway, just an FYI for anyone doing the same project.

The 68 to 70 B body heater cores all have shorter heater hose nipples making it a pain to hook up. Glenray is very reliable and does great work. I have a spare core done by him.
 
Well, I mispoke when I said it fit perfectly. I had to grind off the corner of the notch in the mounting plate. And the tube bracket was welded maybe 1/8" too far forward. It will work. But certainly not a perfect fit.

Good idea using the bicycle tire. I'll remember that for next time.

Follow up question on this box I am working on. There is a small circuit board looking thing with coil wires attached. What is the function of that piece, and can I test it with a ohm meter?

Thanks.
 
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