Abstract: A cooler for air in a pneumatic brake system which includes a thermostatically controlled bypass is provided. The cooler includes a chamber which has an air inlet, an air outlet and a cooler outlet. The cooler also includes an air delivery which is in fluid communication with the air outlet. A cooling passageway is in fluid communication with the cooler outlet and the air delivery. A valve mounted within the chamber is biased to a closed position placing the air inlet and air outlet in fluid communication and is movable against the bias toward an open position placing the air inlet in fluid communication with the cooler outlet. A thermostat is mounted within the chamber such that when air entering the air inlet is above a predetermined temperature the thermostat moves the valve against the bias toward the open position to direct air through the cooling passageway.