A thermostatic valve for controlling the temperature of the coolant in an internal combustion engine controls the flow of coolant between the internal combustion engine and a heat exchanger. The valve includes an actuation element which functions in a temperature-dependent manner for actuating lift of a main valve and of a bypass valve in a valve housing. The actuation element has a stationary piston supported on a valve housing part. A housing can be displaced relative to the piston and on which the valve members of the main valve and of the bypass valve are arranged. Further provided is a monitoring device for the position of the main valve, which works in a contactless manner and which has at least one sensor element contained in the valve housing part, and at least one associated permanent magnet for generating a magnetic field to which the sensor element is exposed.