I'm curious and would like to know:

[Steve Bryant]

Block heaters (immersion heater, engine heater) are installed in the block in place of one of the core plugs and are designed to heat the coolant to a temperature that allows easy engine turnover for starting in very cold conditions.There are also in hose heaters that are installed in the lower hose and circulate the coolant from the heating action. These are very efficient at heating the engine. On small cars such as a mini a block heater will warm things sufficiently to actually register on the temperature gauge !

Cheers,
Stephen (wishing it was warmer )