I just replaced the factory original heater core in my 02 Blazer exactly 1 year ago.
Now it's leaking inside the AC box again.

I took a look at this thread in hopes to find out why my heater core failed.
https://blazerforum.com/forum/2nd-ge...er-1939/page3/

Looking through this site's archive, heater cores failing seem to be a common problem.

I already know how to replace it. I'm looking for answers as to why it failed so I can fix that problem.
I've already gathered that a faulty radiator cap and electrolysis may be suspects.

Any other thoughts?

 

Does Walmart brand 50/50 coolant have anything to do with it?

 

I've also been reading about pressure to the heater core being one possible issue. Would it be safe to install any kind of water control valve inline to the heater core, or would the built-up pressure before the valve be damaging to the water pump?

 

I've seen so many fail (two in my own Blazer) that when swapping the third in I had the first one that failed done by a radiator repair shop instead of buying another crappy OEM one.
Worked for more than 10 years but ultimately failed again. Seemed cracked. I'm not sure if it is vibration from the hoses or as you suggest corrosion.

During the repairs the heater cores looked just fine inside. Mine always leaked at the lateral casings, never in the heater core itself.
Repaired the one which held for 10 years last year (2019) again. The guy who did the repair also soldered a piece of copper in between the tubes which gave them more stability.
In the future when swapping the engine I will definitively replace it with a custom made heater core. I've been thinking on adding hoses through the firewall and fit them on the heater core instead of the two long pipes.

To that valve question: The heater core needs to resist the full pressure and volume in any case. The location of where it taps into the cylinder head suggests that you could run into local overheat troubles if blocking the flow. When swapping my engine - hopefully next year - I will add a three way valve to bypass the heater core altogether without obstructing the flow from the cylinder head to the water pump.

 

As far as I know my Blazer's heater core has never been changed...for sure not in the 12 years I have had it. (knocking sound on wood)

 

Pretty sure mine hasn't either. If it ever starts leaking, I'm going to bypass it and start wearing a coat.

 

As far as I know, mines original, I needed to flush it a few times, but no leaks...

sorry it's not useful, but hope that it's not a continuous problem