Abstract: A combination internal combustion engine and electrolyzer for producing hydrogen and oxygen gases from water on board a motor vehicle in order to supplement the gasoline fuel for the engine further includes a heat activated engine such as a Stirling engine to provide the electrical current necessary to decompose the water, the Stirling engine being activated directly from heat derived from the exhaust of the internal combustion engine. The oxygen and hydrogen gases formed by the electrolysis of water are passed to the air intake of the carburetor of the internal combustion engine and enable the use of a much leaner gasoline to air mixture to run the engine thus increasing gas mileage and reducing air pollutants formed by the internal combustion engine.