CUCV cab heater core multiple failures resulting in leaking of heater core into cab

bimota

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Ok, I've replaced three heater cores in my M1031 this year - time to solve this issue. New cap, good hoses, new heater core works fine (no leaks) for about 6 weeks then starts leaking. Napa heater core replacement three times - Napa says I don't get any more free units under warranty.

So why in the world would my truck blow heater cores? I do drive on the freeway a lot - 55mph for 3-5 hours at a shot but that in itself can't be the cause.

Any suggestion - ideas? This is a great, reliable low mile truck - driven 4-5 times a week for work on remote projects - need that heater to not leak.
 

doghead

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BAd headgasket causing it to rupture? Pressure test it?
 

Adrian A

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Electrolysis may be a problem. Check to make sure that you have plenty of good clean grounds. Your heater core may be an anode that is dissolving first. A multi meter may be able to help you test for current flowing through your coolant. Perhaps someone with electrical expertise can elaborate some more. I know of it. But not how to fix it. Perhaps a sacrificial anode attached to the radiator cap? Is it a pinhole leak in the core?
 

juanprado

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In 20 years selling parts, I have seen batches fail. It would not be uncommon to see a whole production have a failure especially with China stuff.

When I first started selling parts Chloride came out with the sealed gel "torque starter" battery. Brand new idea and the first ones out with it in the early 80's. High cranking amps and could be mounted side ways etc. Expensive and sold well. 12-18 months later they all came back defective & more predictable than an Australian boomerang. The first generation had not filled them with enough jellied acid to last. Things happen.

As a former NAPA store manager and Distribution warehouse manager for 10 years, I can tell you there is no such thing as a return limit. A company owned store or independent jobber can return that heater core a zillion times and NAPA distribution center will issue credit. Something about "customer Service" and the customer is usally right. :)

I do suspect you have a bad part and would not use the same ones again. Time to source it from a different company with a different supplier.
 

WARWAG

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Check your engine block ground. I just replaced my heater core. I have the original and will have it fixed at me local Radiator shop. BUT, I did notice that my coolant light started coming on a few months before I had my first leak. After reading up on the causes other than age a bad ground seems to cause this type of issue. So I plan on checking my engine block ground sometime next week. The coolant light might be a bad sensor. It could just be a coincidence......... Who knows but check the block ground and go from there. As far as the NAPA replacement core all I can say is its CRAP. Yes it works but the original weighs in 4 times as much. It brass or bronze and not that ultra thin walled aluminum Chicom crap that NAPA is selling. If I had to do it over I believe SUMMIT RACING sells a much better heater core.
 

Skinny

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You can check for proper grounding by opening the radiator cap and sticking in a DVOM lead to measure voltage drop to ground. I want to say anything over 0.1v DC is bad but I would google the procedure to become more familiar with it. I agree with everyone...sounds like electrolysis or a defective batch. This is why I spent $120 having my OEM unit recored.

Good luck and Happy Turkey day everyone!!!
 

MarcusOReallyus

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Electrolysis may be a problem. Check to make sure that you have plenty of good clean grounds. Your heater core may be an anode that is dissolving first. A multi meter may be able to help you test for current flowing through your coolant. Perhaps someone with electrical expertise can elaborate some more. I know of it. But not how to fix it. Perhaps a sacrificial anode attached to the radiator cap? Is it a pinhole leak in the core?


Yes, but .... with a correction. This is often called electrolysis, but that's NOT the correct term. It's galvanic corrosion. It's a huge problem in the maritime world, and any ship mechanic should be very familiar with it.


You can check for proper grounding by opening the radiator cap and sticking in a DVOM lead to measure voltage drop to ground. I want to say anything over 0.1v DC is bad but I would google the procedure to become more familiar with it.

Yep. One end in the radiator water, and one on the battery ground. In a perfect world, you'd measure zero.


If that's the problem, you may not win the warranty battle. Here's what you do to fix the problem. Yes, check all your grounds, clean them, make them nice and shiny.

But now ADD a ground wire from your heater core to a good ground location. I'd take it right to the battery. Also do the same with your radiator. Use something like 14 or at least 16 gauge wire. Make sure those connections are nice and bright, and coat them with either dielectric grease or conductive grease.

The idea is to make SURE that all of your cooling system components (engine, radiator, and heater core) are at the same electrical potential, that is, at ground potential.


There are radiator caps sold that have a sacrificial anode built it, and the zinc part of it is replaceable. I've also seen zinc plugs that replace your radiator drain. Not really expensive, either. I'm putting one on my family van this weekend.
 

WARWAG

Active member
Just checked. One lead on the ground and the other touching nothing 0.01. One lead on the ground and the other in the radiator fluid 0.22. NASA we have a problem. I suspected this and was planning on cleaning and greasing up the connections with conductive grease anyway. I will report back after all the grounds are done.
 

bimota

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Hard for me to believe galvanic corrosion would take a heater core out in a few weeks but I'll check it - interesting if nothing else. Bad batch is also out because I popped the original factory one as well. One mechanic told me I am revving the engine to high by driving 60mph - which I know is BS but hey - mechanics these days. Anyway I did buy a Tiny Tach because I want to know hours and rpms - trying to decide if I should keep this truck or sell. Around town, working remotely, towing etc is all great but the freeway ride is simply painful.

Anyway - back to the heater core - any more ideas? I bought a used factory unit but I'm nervous to put it in without a solid solution. Is there a drawing or detail on how the hoses need to be run - not sure why that would matter but these could have been changed somewhere in the last 25 years on active duty.
 

doghead

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You could try adding a ground wire between the core and a good body ground?

Have you ever checked your coolant PH level?
 

tbearatkin

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Had a friend that kept going through accelerator cables they kept breaking. It was a bad ground causing it. This was on a British made vehicle but no reason to believe it would not do the same thing on an American one.
 
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