Abstract: A coolant temperature control system for an internal-combustion engine in a motor vehicle having an electrically heatable thermostatic valve whose method of operation can be shifted by electrical heating in the radiator operation direction. Control devices are provided for recognizing a defect of another system in the motor vehicle which controls the coolant flow. When a defect of this other system is recognized, the thermostatic valve is heated. Particularly when a defect is recognized, the heating of the thermostatic valve is controlled such that the coolant temperature is maintained below a preset coolant temperature threshold. Preferably, the recognition of a defect is carried out by means logically monitoring output signals of the other system.