The vehicle fuel preheater works on the known fact that by preheating the fuel, the fuel is more effectively vaporized, resulting in more efficient combustion. This preheating is accomplished using heat that normally cycles through the heater core for interior heat. The preheater, i.e., heat exchanger, has a housing, through which heated engine coolant on its way from the cooling pump to the heater core is routed. A coiled copper gas line is routed through the housing, and is connected between a segment of the fuel line and the engine combustion chamber so that the preheater can deliver preheated fuel to the combustion chamber. The heat exchanger is installed in a vertical orientation to prevent air lock in the fuel and cooling systems.