m939 Heater Core

Sprung a leak today in my heater core during a parade in my m923. I see the heater core has a special vent fitting but I am wandering If anyone has picked up an aftermarket heater core that works in the m939 of the same dimensions and hose hook up orientation.

I suspect it would be without that fitting and work ok.

I searched but did not see anything if anyone can point me in the direction?

Thanks,

I am in the same boat. I have a parts truck so I took the core from that but although no leaks it does not look much better than the one I took out. I was advised by another member that a late 80s Chevy s10 core will work. The s10 one is a little thinner but does fit width wise. It sticks out the side about 2 inches I'm not sure if it can be cut down and the end caps resoldered on. I found some new cores on the bay they were very expensive and were a slightly different configuration than mine though. I believe the petcock is a drain or air purge I think the truck would be fine without it though. If you come up with something better please let me know. It's cold here in CT in the winter I like my heat.

I will probably pull it tomorrow and play with it. I used to work parts for 20 years so I know my way around a buyer's guide and illustrated parts manual unlike the youngsters today at the stores who can only punch buttons.

I will definitely share whatever I find.

My interpretation of cold is way different than yours considering where I live I could not operate in your lz

I had my heater core start to leak. I took it to a radiator shop and they replace the core. I guess there is a replacement core that works.
Looks just like new.

JUANPRADO, you are in LA and it is b**** hot much of the year...and fairly mild the rest, right? Does it really get cold enough to warrant a heater? Just curious. Jason Frisch (HALFTRACK), also located in Metairie, removes his heaters as soon as he gets a truck for this reason. I'd check with him because he probably has a few sitting around that you could use for parts. Good luck.

I'm sure a radiator shop could make a custom one. It's a heater core not a flux capacitor.

If you don't find a alternative, I have a complete heater unit left over I'll sell cheap.

Edit: this post is over 2 years old, the heater is long since gone.

BKubu said:

JUANPRADO, you are in LA and it is b**** hot much of the year...and fairly mild the rest, right? Does it really get cold enough to warrant a heater? Just curious. Jason Frisch (HALFTRACK), also located in Metairie, removes his heaters as soon as he gets a truck for this reason. I'd check with him because he probably has a few sitting around that you could use for parts. Good luck.

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We did get to 50 a few mornings ago considering avg temp seems to be 100 I meant humidty also year round. We all have to endure I know

Thanks for the lead.

I will keep you in mind Drew but Jeff is also not too far from me and I suspect he still has some cabs if I do not come up with a match.

I could not find a procedure in the tm for just the heater core removal just the whole heater box.

It is not necessary to pull the whole box.

Unbolt and move the heater control cable and bracket
remove the 2 bolts holding the diagonal brace closest to the engine to the firewall
remove the bolts holding the box to the inner most diagonal bracket. The spin on t-filter will just drop down
remove the diagonal and support brace.
Remove the lid on the box facing the engine where the hoses come out with 4 bolts.
Pull off the hoses and unscrew the bleeder.
The heater core slips out towards the engine. Plenty of room to move it out.

The point of failure appears to be that the core stands up right in the box with no padding or insulation. It looks like my bottom corner sprung a leak probably from bouncing around and rubbing on the bottom of the box. Only thing that appears to hold it rigid is a rubber bushing inbetween the tubes on the removable box lid.

I will add some sticky taped universal foam to the core to cushion it when I reassemble.

Too late to go to the NAPA store where I used to work so I will go tomorrow to try to match and also to a radiator shop to check on a repair price.

OE is made by hunter defense technologies. I will send them a tech email and see if they reply?

The petcock type fitting is for bleeding air out of the system after refilling it. At Fort Riley we had a 5-ton that had everything hooked up but just refused to blow heat, just cold. We bled a bunch of air out of that fitting & she blew hot as you please. Truck had been in the field for a week & that core never flowed enough to displace that air the whole time.

I have to pull the core in one of my M931 tractors, it sprung quite a leak also .

The heater is tagged original stock 12255989-1, Model HW 30-4

I have attached a product sheet on it.

Hunter tech did reply to my email with contact information to their distributor that could help me with a heater core:
Jim McMath of Windward Enterprises 843.897.3120 jmcmath@windwardent.com
Price was a wopping $175

I tried to match one up but was very disappointed to find most are aluminum with plastic tank caps and almost all made in China and for the most part look cheap. When I sold parts, One of the biggest mistakes I saw was the plastic and aluminum radiators that replaced good ole fashioned metal. They just don't hold up to the repeated thermal cycles of hot / cold and the plastic tanks will break. It is just a question of when. I have had had 4 personal aluminum automotive radiators fail in the last 20 years and consider them junk.

I went with the suggestion of having it repaired at a local radiator shop for $30.
If it lasted 30 years, I am confident it will last a while longer with a minor repair.

175 does not sound bad if you look at what people are trying to get for them on the bay.

Heck, I'd part with the heater box I have for way way way less than that.

My truck was rebuilt in 2010 and a new heater box installed then. They dont seem to last long. Not that they are hard to change its just annoying to have coolant pouring into the passenger footwell.

I had a leaking m939 core as well. The 809 series trucks use a slightly different core and I couldn't find any nos parts. I also ended up having
a radiator shop repair mine. 2 years later it still works fine.

Suprman said:

175 does not sound bad if you look at what people are trying to get for them on the bay.

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Yeah, it is crazy priced. Uncle pays $615 for the whole unit. Nice profit for a sheet metal box, heater core, bower motor & wheel, and the fresh air flap. Must be some crazy money in defense contracting.

Install went smooth and I burped the air out of it with the bleeder screw.

I noticed after referencing the tm that my hoses were backwards. I had marked them when I took them off so they appear to have been mis installed at some point.

The heater core inlet tube is the one closest to the firewall & points down. The hose connects to the fitting that is on the oil cooler housing.

I have attached the tm diagram. I found it interesting that the water starts low and is pushed uphill.

Has anyone found a complete engine water flow chart through the engine , radiator, and all the coolers?

I just had my 2010 rebuilt M936A1 blow the heather core into the cab. Spent hours looking in the TM for a R&R procedure and nothing...thanks for your thread and instructions on the R&R. I guess I'll see how bad it is and try a radiator ship first too.

patracy said:

Heck, I'd part with the heater box I have for way way way less than that.

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I just wanted to bump this, I still have it... CHEAP. Way cheap.