Engine Block Heater: Operation
WARNING: This page is about a different car, the 2006 Dodge Magnum, 2006 Dodge Charger, and 2006 Chrysler 300. 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.