A variable coolant pump for a cooling circuit of an internal combustion engine that has a pump housing in which is mounted a hollow shaft that is driveable by a pulley. At one end of the hollow shaft an impeller is fastened which has vanes projecting into an inlet chamber and which is firmly connected via axial bridges to a cover disc. Through rotation of the impeller together with the cover disc, water can be sucked into the inlet chamber via an inlet connection piece of the pump housing and conveyed by the vanes into an annular passage of the pump housing. A guide disc with a contour corresponding to the impeller is further arranged between impeller and cover disc. The guide disc is guided by the axial bridges and can be displaced axially via a positioning unit by a piston located inside the hollow shaft.
