M939 heater core bypass

[FBPD1315]

I have an M939 and the heater core is leaking pretty badly. As a temporary fix I want to bypass the heater core. Are the petcocks on the block where the hoses connect to close it off? They appeared to be loosened (open) all the way so I tightened them all the way however the heater core still leaked. It definitely wasn't just residual fluid coming out because I closed them when the engine was cold and then as it got up to temp it started leaking. So I'm guessing that the petcocks are not what I thought they were for or am I missing something?

 

[CARMAN]

I have an M939 and the heater core is leaking pretty badly. As a temporary fix I want to bypass the heater core. Are the petcocks on the block where the hoses connect to close it off? They appeared to be loosened (open) all the way so I tightened them all the way however the heater core still leaked. It definitely wasn't just residual fluid coming out because I closed them when the engine was cold and then as it got up to temp it started leaking. So I'm guessing that the petcocks are not what I thought they were for or am I missing something?

I use those in the summer to kill the heat in the cab and it works. Otherwise you roast. Would assume they should stop all fluid unless yours don't close all the way.? Since yours won't stop I would just separate there and splice them together for now.

 

[FBPD1315]

Thanks for the reply. That's what I plan on doing next. I tightened them by hand because it didn't want to strip any threads so maybe they just aren't closed all the way but they sure do look like they are. Is there any visible thread left when you close yours?

 

[CARMAN]

Honestly can’t say. I just reach in there and turn them till they stop. Will not be with the truck for a few days as it’s not at my house. Can take a peak but in the mean time give them a little twist with some pliers.

 

[therooster2001]

They should definitely stop all flow. Mine leaked (twice now) and I've shut them off for good (yes, no heat in the winter) It is possible that the valves let through something, as stated, just join them together if it won't stop. Those valves are the best idea ever, and mine are all hand tight.

 

[simp5782]

The original brass heater cores leak pretty easy. Even the NOS and Roman ones. The Murray units from O'Reillys seem to hold up well

 

[juanprado]

A simple way to bypass if the valves are not working is to splice the 2 rubber hoses together with a fitting or piece of pipe.

 

[wiersema07]

Bring back old thread but I’m in same situation and wondering if any knows a part number for one of these
Second question is will this nut just come out from the part that hose connects to or do I need to disconnect hose n pull the whole piece from block ? The wing nut part fell off n just spins n heater box still leaking when pressure tested. Not I have both sides of radiator leaking through the gaskets by bolts so I’ll need to take those sides off n try n put cork gasket in with some rvt high temp gasket sealer all over it n hope it’ll seal or I’ll need new radiator n def don’t want that cost

 

[wiersema07]

Bring back old thread but I’m in same situation and wondering if any knows a part number for one of these
Second question is will this nut just come out from the part that hose connects to or do I need to disconnect hose n pull the whole piece from block ? The wing nut part fell off n just spins n heater box still leaking when pressure tested. Not I have both sides of radiator leaking through the gaskets by bolts so I’ll need to take those sides off n try n put cork gasket in with some rvt high temp gasket sealer all over it n hope it’ll seal or I’ll need new radiator n def don’t want that cost