Abstract: A fuel and air mixture expanding and preheating system for use in a vehicle having an internal combustion engine, an intake manifold, a carburetor, an automatic transmission and a transmission fluid cooler includes a heat exchanger body having a first mounting plate dimensioned for attachment to the carburetor and a second mounting plate dimensioned for attachment to the intake manifold. A heating fluid inlet of the heat exchanger body is dimensioned for connection to a heated automatic transmission fluid line of the vehicle, between the automatic transmission and the transmission fluid cooler. A heating fluid outlet of the heat exchanger body is dimensioned for connection to a transmission fluid cooler inlet of the vehicle. A throttle valve is mounted in an outlet portion of the heat exchanger body, adjacent the intake manifold mounting plate.