What is "block heater"

n. An electric heater that heats the engine of a car to ease starting in cold weather.

A block heater warms an engine to increase the chances that the engine will start as well as warm up the vehicle faster than it normally would in extremely cold weather.

The most common type is an electric heating element in the cylinder block, connected through a power cord often routed through the vehicle's grille. The block heater may replace one of the engine's core plugs. In this fashion, the heater element is immersed in the engine's coolant, which then keeps most of the engine warm. This type of heater does not come with a pump. They may also be installed in line with one of the radiator or heater hoses.

Block heaters that run directly on the vehicle's own gasoline or diesel fuel supply are also available; these do not require an external power source. The coolant is heated and circulated, usually by thermosiphon, through the engine and the vehicle's heater core.

Heaters are also available for engine oil so that warm oil can immediately circulate throughout the engine during start up. The easier starting results from warmer, less viscous engine oil and less condensation of fuel on cold metal surfaces inside the engine; thus an engine block heater reduces a vehicle's emission of unburned hydrocarbons and carbon monoxide; also heat is available more instantly for the passenger compartment and glass defogging.

Block heaters or coolant heaters are also found on permanently installed systems using diesel engines to allow standby generator sets to take up load quickly in an emergency.