A coolant regulator is provided including a housing having a coolant chamber and a rotary vane arranged therein, a drive shaft leading out of the coolant chamber that rotates the rotary vane, and a shaft seal which seals the coolant chamber from the surroundings. The shaft seal seals against a housing inner lateral surface of a housing recess and sealingly encloses the drive shaft. An end portion of the shaft seal facing the rotary vane is a circular ring that, under elastic deformation of the bead thereof, seals against the housing inner lateral surface on the outer circumference and encompasses a spreading ring on the inner circumference that limits an axial shift of the shaft seal toward the rotary vane to a dimension d