I have here a Heater Cure issue I've been trying to set time aside to deal with.
It's leaking inside the heater box, but I have no idea how it is and where in the aluminum piping it could possibly leak.

This problem started back in 2019. The factory OEM heater core started leaking inside the heater box. I knew it was because I saw a pool of coolant on the garage floor and I can smell it in the A/C. I pulled the dashboard out to replace it that same year with an aftermarket heater core I got from Advanced Auto. This one went leak-free for barely a year until I started seeing coolant on the floor again and could smell it in the A/C again. The new one from Advanced Auto somehow failed in the same exact way as the factory OEM one in late 2020.

This past September, I had time to work on pulling the dash board out, but I was convinced at the last minute to pressure test just the heater core before taking everything apart. I did a cold pressure test and it held it just fine. So, flushed everything and reconnected the heater hoses to the core removing them from bypass. This is where it gets weird. After a couple weeks driving, I began smelling the strong coolant odor again, and noticed the pooling on the garage floor again.

I just don't get it. It holds pressure when it's tested, and when just running the engine in place trying to cycle the coolant there is no leaking. But when the truck is driven normally at operating temperature for several miles, the heater core starts leaking. Only while it's hot, never cold. How can this be?

It's definitely not a bad hose clamp and coolant leaking through the slot in the fire wall. I installed new clamps, the hoses are new, and I duct taped the opening for good measure. In whatever which way it's leaking, the aluminum piping on the inside is somehow compromised (on a brand new heater core), and I don't know how.

Can too much pressure cause this? High pressure and high temperature? I had a 16 PSI radiator cap when the leaking started happening the second time in 2020. I then swapped it for a 15 PSI cap thinking that pressure being too high was part of the failure. If pressure is the problem, how would an in-spec water pump be causing that? Would installing a flow control valve help a high pressure problem? I'm tempted to install a flow control valve, but it seems unecessary since the factory config never had one.

 

I had similar symptoms at around 150,000 miles thinking it might be the heater core but it turned out to be the LIM gaskets leaking at the back of the block.


George

 

Hmm... I'll check out the LIM, but I'm pretty sure it's fine. The leaking stops and I retain a full reservoir tank when I bypass the heater hoses.