Leaking Heater Core

[Computerdoc08]

My heater core looked like it started leaking so I replaced the entire blower / heater core with NOS as the blower wasn’t working anyway. I also replaced the hoses and clamps. Started the truck and it looks like the NOS unit from 1985 is leaking too. Is there any other problem that could cause coolant to leak from the heater core that I’m missing?

 

[Mullaney]

My heater core looked like it started leaking so I replaced the entire blower / heater core with NOS as the blower wasn’t working anyway. I also replaced the hoses and clamps. Started the truck and it looks like the NOS unit from 1985 is leaking too. Is there any other problem that could cause coolant to leak from the heater core that I’m missing?

.
Loose Clamps?
Is one hose larger than the other? Maybe the hose is too large to fit onto the "stub" that you attached the hose to?

 

[Computerdoc08]

The clamps are pretty tight, but I will definitely check. I didn’t see any coolant near the stubs, only in the bottom of the box.

here is the spec on the hose I used.

5/8 Inner diameter (epdm, 95psi rated) Gates Green Stripe Heavy-Duty Heater Hose

 

[msgjd]

other than what's already been mentioned in this string,, how about a slight leak from the bleeder valve or its threads?

 

[Computerdoc08]

I didnt see a leak at the bleeder, but tomorrow I will remove the top cover on the heater core housing and idle the truck so I can see exactly where it may be seeping from.

 

[Computerdoc08]

Today's update: I removed heater core from the truck and applied permatex sealant between the petcock and the core. I rinsed the outside of the core off and refilled with coolant and water. I'm going to let it sit overnight in an upright position and see if I get any leaks. I'm going to drop the original leaking core off to a radiator shop so I may be taking 2 with me...

 

[HDN]

This is interesting. My M35A3 has a leaky heater core too, and from what I know many M44A3 trucks came out of the factory with leaking heater cores. I'm having trouble finding the posts here though - I'm pretty sure I read about it here Those trucks were built from 1995 to 1998.

Fortunately I only drive the truck when it's warm enough outside I don't need the heater anyway - no winter driving for me, especially with the salt up here! One day I'll pull that core and take it to a radiator shop for a repair.

 

[Computerdoc08]

Being in Florida, I’ve only used the heat once. I verified my NOS core is leaking so 2 cores to the rad shop tomorrow, then I’ll have a spare.

Has anyone used the new heater cores I’ve seen online? They look slightly upgraded.
Heater Core Upgraded?

 

[Computerdoc08]

Well…. The radiator shop called and said he can’t fix either core, so I guess I’ll need to try one of those new cores out.

I know the cores are pretty basic, but does anyone have a military radiator expert that may be able to work some magic on 2 heater cores?

 

[HDN]

Well…. The radiator shop called and said he can’t fix either core, so I guess I’ll need to try one of those new cores out.

Can't fix the core or doesn't want to fix the core? I'd try another shop for a second opinion.

This kinda news just makes me want to try and fix radiators myself.

 

[Computerdoc08]

I’ll be taking them to a shop in Tampa to get a larger shops opinion.