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There is an open knockout on my 51 M37, passenger side of the cab, right in front of the lower door hinge. It looks like a giant keyhole. Probably 6" tall. There is only a couple of inches of space till the inner side of the cab, and no hole out the bottom etc. Anyone here know what it was for?
Thanks,
Tim

Tim,

That knockout was for the Arctic Powerplant heater kit. It had a shroud around the oil pan and a warming plate under the batteries. Basically the exhaust from the heater warmed the engine oil and coolant circulated through the heater warming the plate under the batteries.

Cabell Garbee has pictures of the manual on his website: http://www.garbee.net/~cabell/arcticmanual.htm

On the scan manual cover, you can pick out the heater box mounted below the gas can to the left of the passenger side fender.

--Steve

Hi Steve,
Wow, installing that setup is pretty involved! Thanks for the link, it made for some good reading. My knockout is gone, but not because the arctic heater was ever installed. Probably some idjit wondered what was behind it!
Thanks again,
Tim

It would be an interesting project to install one, but looks like a lot of work. I think one of the guys on here (SydneyM37?) actually had one on his truck.

This page shows the hoses that went through that keyhole knockout, into the cab and then through the floor into the engine compartment:
http://www.garbee.net/~cabell/Otherfoll ... %20028.jpg

Yeah, a lot of work, and none of the heat goes into the cab!
Really is an Arctic accessory.
Tim