Abstract: An auxiliary heater controller is provided for use with a liquid cooled engine which includes two fluid circuits. The first fluid circuit includes the engine, a heat exchanger with an air flow creating fan, a heater and a pump, while the second fluid circuit shunts the engine and includes only the heat exchanger, heater and the pump. A single two-way valve operates to direct fluid to either the first or the second fluid circuit, and a timer unit is provided which operates automatically at a preset time to cause fluid to flow in the first fluid circuit for a predetermined time period. The air flow creating fan is operated by a thermostat at low speed when the engine is not operating and is operated by a manually controlled variable speed control unit when the engine is operating.