Abstract: This invention pertains to a controller for electric heaters for preheating temperature sensitive components of internal combustion engines operating in very cold climates. The controller reduces energy consumption by turning on the engine component heater no sooner than necessary for the object to achieve the desired temperature. The device monitors ambient air temperature and when it is cold enough, projects the rate of the change of temperature forward to predict the temperature at the time the engine must next be started. Using manufacturers' heater specifications, the air temperature ambient to the engine components and an heating function derived from heat conduction theory, the device calculates the amount of time required for heating the engine components and turns on the heater when the appropriate time arrives.