A coolant pump assembly for an electric vehicle includes a positive displacement pump having an inlet port, an outlet port, and a rotor, a variable-speed ac motor having a rotatable shaft mated with the rotor of the pump for rotating the rotor of the pump to circulate coolant through the inlet and outlet ports of the pump, and a motor control unit, communicating with a DC power source of the electric vehicle, for controlling the speed of the motor to provide a variable coolant flow through the electric vehicle.