In an electrical coolant pump, preferably for use as an additional water pump in a vehicle, a radial bearing of the shaft is provided by means of a radial slide bearing lubricated with coolant on the separating element which is disposed between the pump impeller and the rotor. A dry-running electric motor has a radially inner stator and a radially outer rotor is accommodated within the motor chamber. A shaft seal is disposed between the radial slide bearing and the motor chamber. The rotor is formed in a cup shape, the inner surface of which faces the shaft seal and is fixed to the shaft in an axially overlapping manner. The motor chamber has an opening to the atmosphere which is closed by a liquid-tight and vapor-permeable pressure equalizing membrane. The separating element is configured as a support flange with a separating portion and an axial projection into the motor chamber, to which the stator is attached. The control unit is disposed between the separating element and the stator in the axial direction.