A coolant controller for a coolant circuit of an internal combustion engine has a housing and a thermostat valve arranged therein. The thermostat valve has at least one valve closing member loadable by a working element as a function of a temperature value, a temperature sensor as well as a heating element for the working element. The housing is provided with at least one plug from which connecting lines extend to the temperature sensor. A current supply for the heating element is present. The plug, the temperature sensor, the connecting lines and the current supply for the heating element are provided as a pre-manufactured assembly and this assembly is integrated into the housing.