Engine Block Heater: Operation
WARNING: This page is about a different car, the 2004 Dodge Intrepid, 2004 Chrysler Intrepid, 2004 Chrysler Concorde, and 2004 Chrysler 300M. However, it is still accessible from the selected car via links, so may be relevant.
When power is applied (110 volt AC) to the block heater, the heating element transfers heat through the aluminum engine block and into the coolant without directly penetrating the cooling system.