Cold Outside Air Through Firewall

[richingalveston]

I would think the truck would not run for an hour with a stuck thermostat.
Is this a new problem that only happens with very cold weather? if so you may need to put some cardboard in front of the radiator

 

[cucvrus]

You may have already checked this. But make sure your heat temperature blend door is operating properly. i have seen the cables flex and bent and the blend door be stuck in the partial open position. this may not be your case but it is worth a look see. Another option. Is find a civialian diesel truck of the same year and remove the under hood insulation on the firewall and install it on your CUCV. Probably easier said then done but it is not impossible.

 

[MarcusOReallyus]

I would think the truck would not run for an hour with a stuck thermostat.

That depends whether it's stuck open or closed. If it's closed, yeah, it will be fried a long time before an hour. If it's stuck open, it will run for years that way.