Abstract: There is disclosed automatic means for limiting the operating temperature of an internal combustion engine that includes a pyrometer to sense the exhaust gas temperature from the engine and generate a signal therefrom, a temperature controller having an adjustable, maximum set point temperature to receive the signal from the pyrometer and to generate a control signal which is applied to a control valve in the fuel system to the engine or to electromechanical means to limit the supply of fuel or governor control in response to a sensed exhaust gas temperature which exceeds the preselected, maximum set point temperature. The invention can be particularly applied to a diesel engine by installing a flow control valve in the diesel engine fuel system operative to cycle the valve when the exhaust gas temperature exceeds the preselected maximum, set point temperature.