A valve fitted with a housing which comprises at least two mutually apart coolant hookups, and a thermally expansible device, including a housing and a push-rod and resting on the housing and operating in concert with a valve element that in turn operates in concert with an annular valve seat, said valve seat being situated between the two hookups, and a spring that biases the valve element toward the valve seat, wherein the valve element is in the form of an annular valve disk made by two-part injection molding, where one annular sealing portion is made of an elastomeric plastic and the remaining valve disk is made of a hard plastic, the outer sealing portion cooperating with the valve seat and the inner sealing portion cooperating in a sealing manner with a housing of the thermally expansible device.