Abstract: A preheater for aircraft engines utilizing as a source of thermal energy hot water from an automobile. The preheater is comprised of a portable housing having a radiator through which hot water from an automobile engine is circulated. A fan in the preheater energized by an electric motor having leads attached to the battery terminals of the car battery pulls air through the radiator of the preheater and is heated and then discharged by the blower fan through hot air ducts which are inserted in the air intake or nose wheel opening of small aircraft to heat the engine and oil sump in cold weather and facilitate the starting. The preheater is provided with a special valve which is inserted in the car and has a three-way position interrupting the hot water hoses to the car heater from the car radiator and a return hose to the pump.