Originally Posted by HeritageHighRoof
I thought the block heater manufacturers warned against this because the rapidly moving coolant by the heater element could create an air pocket that could allow the element to overheat.
News to me. An air pocket around a heating element designed to heat liquids typically causes rapid failure of the element ... as in a minute or less. There is some convection movement of coolant due to the heating, but it's not much, and the location of a block heater in the block is relatively low and "wet" ... it's installed in place of one of the block's frost plugs.
Block Heaters in Canada typically outlive the car, and no car leaves the factory for CDM vehicles without one (it's on the option sheet, but you're paying for it as it's installed and the dealer won't delete it), so I don't think this is a real problem. They've been standard factory equipment in Canada since the 1960's (original application was a performance part on Gen II Corvettes, but quickly became standard equipment on all vehicles delivered to Canada).
They are not particularly hot elements in the first place ... gasoline engines use either a 400 watt (4 cyl), 600 watt (V6 and smallblock V8s) or 750 watt (big block V8's, V10's) unit, and even diesel engines are only 1000 watts (they won't physically fit in a gas engine). A 15A circuit is 1800 watts and even allowing for extension cords (eg, typical circular saw) they still can safely provide 13A (1560 watts).
To get an idea of the heat energy they provide, it takes three hours to warm a car's coolant level to the point where the heat lost is equal to the heat added at below freezing temperatures.
