Curious 'original' red canister in heater core hose line

[slowpatina]

I'm curious what this cannister is for? (a couple pics were unfortunately auto-rotated by our host)

Looks like an original item (possibly dealer installed). For some IIA 88" truck background, it was in Alaska 30+ years, as in cold location.

Lower red hose connects to exhaust side of lower block coolant drain. Upper red hose Y's into the upper (top) heater core hose inlet near the core itself (ie: into same core hose from rear of head).

There are also a few prongs on top of the canister beneath a small flip-up cap, and also prongs on side of block, as if a cable connected the two for the "Thermostatically Controlled" feature noted on canister's front label (other writing under mount clamp is illegible).

Based on upward coolant flow direction (block to heater core) it doesn't seem to be a block heater, but perhaps a more speedy way to heat the coolant and get warm air into the cab more quickly?


Anyone seen this before... any thoughts on the purpose of this old treasure?

)