Hi Svenn
You raise an interesting point about not be able to drain the heater core unit. In reading through the cold weather equipment manual I don't find any reference to this problem or the need to always run antifreeze in heater equipped vehicles. There are numerous cautions about damaging the heater cores and about checking them for leaks.
Has anybody come across a manual or service bulletin referring to this issue?
Great to see actual photos of a heater unit, thanks for posting.
Special Cold Weather Equipment Manual Link
http://canadianmilitarypattern.com/S...0Equipment.htm there was a page missing from this manual in my posting which Svenn spotted and I have now fixed.
Cheers Phil