with regard to the control of the rotational position of the valve element 39 said valve element 39 is connected via mutually jointed link element 40 and 41 around which the previously mentioned compression coil spring 47 is fitted to a hub 42 which is in turn connected to the inside end of a coiled bimetallic spiral strip 43 the outer end of which is connected to the coupling housing cover 23 in which said hub 42 is freely rotatably mounted the link elements 40 and 41 can slide longitudinally with respect to one another but are constrained by their construction not particularly shown to rotate together thus the valve element 39 is positioned with regard to its rotational position by the action of the bimetallic spiral strip 43 i e according to the temperature of said bimetallic spiral strip 43 which is substantially the same as that of the air impinging on said spiral strip 43 which has just passed through the vehicle radiator not shown while on the other hand the axial position of said valve element 39 is not substantially constrained by the above described construction the bimetallic spiral strip 43 is so constructed that when the temperature of the air flowing through the radiator and impinging on said bimetallic spiral strip 43 is lower than a first determinate air temperature value for example 55 u00b0 c said bimetallic spiral strip 43 rotationally positions the valve element 39 to its position shown as 34 a 34 in fig2 so as substantially completely to close the first valve port 33 when.