A mechanically driven coolant pump having a controllable delivery rate for a main delivery circuit from a first outlet and for a secondary delivery circuit from a second outlet of the coolant pump. The coolant pump comprising a hydraulic control circuit which is derived from the coolant pump and has an input-side auxiliary pump, an output-side proportional valve, and a regulating slide for limiting the flow of the main delivery circuit. A cylindrical portion of the regulating slide can be axially displaced in the pump chamber in order to radially shield the pump impeller by means of a pressure in the hydraulic control circuit counter to a restoring force. A regulating valve is connected to the hydraulic control circuit to limit the flow of the secondary delivery circuit, wherein actuations of the regulating slide and of the regulating valve are associated with pressure ranges in the hydraulic control circuit.