A radiator grille actuating mechanism for use on an automobile having a body and utilizing an engine coolant, comprises a radiator grille pivotably mounted on the automobile body, a link mechanism operatively connected to said radiator grille and pivotably mounted on the automobile body, an actuator mounted on the automobile body and operatively connected to the link mechanism for moving the radiator grille between open and closed positions through the link mechanism, and means for actuating the actuator to move the radiator grille between the open position and the closed position in response to sensing of a predetermined temperature of the engine coolant. The radiator grille can be brought to the open position when the engine coolant reaches the predetermined temperature, thus allowing a sufficient amount of air to be supplied to the radiator to prevent the engine from being overheated. The actuating means may comprise a vacuum actuator controllably supplied with a vacuum as from an intake manifold, or a solenoid-operated actuator controlled by an electrical circuit which issues an actuating signal only when the temperature of the engine coolant is detected and the speed of travel of the automobile drops below a predetermined speed.