Abstract: A cooling apparatus comprising an air-cooled heat exchanger, a plurality of louvres to control a cooling air flow passing the heat exchanger, a mechanism for operating the louvres and means for actuating the operating mechanism according to temperature of the heat exchanger. The actuating means comprises a bar having a first end and a second end and being of a material having a considerably lower thermal expansion coefficient than that of the heat exchanger, said bar being attached by its first end substantially at a first end of the heat exchanger, and means for controlling the position of the operating mechanism in dependence on a difference in displacements of the second end.