I need some help on why my heater core keeps springing a leak. I bought the truck back in July and about a month after owning it, the original heater core began to leak. I replaced it with a Spectra heater core from Autozone and that only lasted 3 weeks. Thinking it may have just been a bad part, I replaced it with another Spectra heater core. It just started leaking again this morning after being in the truck for only 5-6 weeks. I'm not sure what's going on with it.

The truck is a 1995 with a 4.9. I replaced the thermostat and coolant shortly after I bought the truck, but I didn't flush it out. I've kept a pretty good watch on the coolant and it's still bright green (50/50 mix) and doesn't appear to have any contaminants in it. Could this be an electrolysis thing?

 

If you had electrolysis going on I'd think you'd have other leaks as well. More likely is that anything AutoZone sells is JUNK! I quit buying parts there at all.

But you can check for electrolysis as well. Don't want to see more than about 250mV (0.25V) if I remember right.

 

6 weeks isn't enough time to rot one from electrolysis.

Where is it leaking at?

Most likely you are pushing/pulling too hard on the pipes, they are the weak spots. Make sure your hoses aren't pulling tight on them too.

Is your radiator cap correct? It is a problem if it holds too much pressure.

 

My money is on this...

 

[QUOTE=LeoJr;15735314]6 weeks isn't enough time to rot one from electrolysis.

Where is it leaking at?

Most likely you are pushing/pulling too hard on the pipes, they are the weak spots. Make sure your hoses aren't pulling tight on them too.

Is your radiator cap correct? It is a problem if it holds too much pressure.[/QUOTE

This is a good theory

 

I agree with the radiator cap but for a dissenting opinion do you have a clog in one of the lines or where the hose going to the block attaches

 

Are the hoses new ?

 

Just to add my 2 cents. As a few people have metioned your hoses, might be a good place to start. Those hoses will swell over time from heat and age and although they might look fine on the outside, they are not.

 

Thanks all for the suggestions. To answer some questions:

1. Yes, I'm 100% positive it's the core itself. I pressure tested the last two and they were leaking at the solder joint between the core and the tank. This new one is leaking into the cab, so I'm pretty sure it's the same thing.

2. I did replace the rad cap right around the time I replaced the OEM heater core. It's a 13lbs Motorad cap. I don't have a tester, so I don't have a way of ensuring it's working right.

3. Hoses are new(ish). They were replaced prior to me buying the truck. They're in good condition.

4. I'm pretty sure I didn't damage the core installing it. The hoses slide on to the pipes pretty easy. The core slides into the housing pretty easy too and doesn't require any manhandling to get the lid back on.

5. Pretty sure it's not electrolysis. I tested it today and came back with a high reading of 80mV and a low reading of 40mV. From what I've read, that's well below safe values.

 

It's not the hoses being old I'm worried about them being plugged or kinked in case it's forcing a bunch of fluid into the heater and not letting it out

Also I'm pretty sure I know what electrolysis is but what causes it and how do I test for it

 

There's a couple things going on with testing radiators. One is stray voltage, the other is electrolysis. The latter is basically the radiator and coolant forming a weak battery, and will cause pinholes or worse. Dissimilar metals and materials - carbon and zinc for example, in the presence of an electrolyte, will produce an electrical current.

Aluminium and steel together and other components immersed in engine coolant can do the same thing. Not sure if this issue can even affect heater cores, probably not in just a couple weeks anyway. Stray current probably doubtful too, though maybe worth ruling out. This is where poor or missing ground straps cause starter current to course through parts not designed to carry electrical current.

http://www.sancarlosradiator.com/Vol...ectrolysis.htm

 

I went through a dozen heater cores with my old engine.
I did EVERYTHING suggested.
Flush the block
Fresh coolant
Fresh radiator
A new waterpump.
Ground wires
Low psi rad caps
NO psi rad caps...
Hoses
Restrictors

I had a cracked head that only opened up under certain conditions. (Backing off after running hard)
It's bizarre that only one point of a closed system will see high pressure.
It's crazy that a rubber hose will hold enough pressure to inflate a heater core to the point I needed to literally pry it out of the heater box.
My radiator/AC guy inherited the business from his father. He's been doing this for 40 years, and he's never seen it.

Flush the system and fill with new coolant.
Do a hydrocarbon test in a couple of weeks.

 

I was going to say, if all else fails, head gasket or as said above; cracked head

 

Just check the coolant for hydrocarbons.
It is quick and cheap.
It might save you a LOT of time and $$$ in the long run, even if it is not the news you want to hear.

 

I did the hydrocarbon test today. The test fluid never even had a hint of changing colors. So no combustion leakage into the coolant system.