Curious 'original' red canister in heater core hose line

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?

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Certainly looks like a coolant heater. Mains 120V 50/60 htz AC . I have seen similar units here in the UK . I wonder if it has a pump in it to circulate the coolant or relies on thermo syphon to generate flow. Either way will also heat the block to some extent
I have an original Rover supplied block heater in my vehicle , screws in place of the alloy plug just above the starter motor . 240 volt as its the UK but they did supply a 120 volt one for export.

Thanks @roverp480. Seems we're on the same page in thought. Will likely leave it in place simply because it's original as is most of the truck. If it ever rusts out then it can be removed and the usual heater core feeds would still be in place.

That is an engine heater....the challenge with them being that eventually they can rust through......don't sign me up for that!!!