An electrically driven coolant pump

A method and pump for heating coolant flowing through a cooling system of an internal combustion engine having an electrically driven circulatory pump (12). The pump impeller (21) is driven by an electric motor (24) having a housing (22) through which a portion of the coolant flow passes, permitting heat exchange between the electric motor (24) and the coolant so that heat generated by the electric motor (24) is used to heat cooling fluid. The flow of coolant through the motor housing (25) is controlled by a flow control valve (31).