A regulation assembly of a water pump group for a cooling system of a vehicle, for example of its engine, positionable downstream of said pump group, wherein the regulation assembly comprises: - at least one inlet port through which the cooling liquid flows in from the pump group; - at least two outlet ports (121, 122, 123) through which the outbound cooling liquid flows; - a regulation chamber located between the inlet port and the outlet ports (121, 122, 123); - regulation means housed in the regulation chamber comprising: i) at least two shutter elements (221, 222, 223) operating with the respective outlet port (121, 122, 123), wherein each shutter element (221, 222, 223) is movable in an axial direction substantially orthogonal to the respective outlet port (121, 122, 123) between a closed position, in which the outlet port is occluded, a plurality of intermediate positions distal from the outlet port and an open position corresponding to the maximum opening of the outlet port (121, 122, 123); ii) a regulation member operatively connected with the shutter elements (221, 222, 223), which extends along a main axis (X-X) and is rotatable about said main axis (X-X), in such a way that one of its respective angular positions corresponds to a predefined position of the shutter elements (221, 222, 223) and thus to a regulation of the quantity of cooling liquid towards a respective duct of the cooling system; wherein the regulation assembly is characterized by the fact that the regulation member comprises at least one control passage that extends around the main axis (X-X) defining portions radially distal from the main axis (X-X) and portions radially proximal to the main axis (X-X), wherein each shutter element (221, 222, 223) comprises a control end (2210, 2220, 2230) engaged to said control passage. - at least one inlet port through which the cooling liquid flows in from the pump group; - at least two outlet ports (121, 122, 123) through which the outbound cooling liquid flows; - a regulation chamber located between the inlet port and the outlet ports (121, 122, 123); - regulation means housed in the regulation chamber comprising: i) at least two shutter elements (221, 222, 223) operating with the respective outlet port (121, 122, 123), wherein each shutter element (221, 222, 223) is movable in an axial direction substantially orthogonal to the respective outlet port (121, 122, 123) between a closed position, in which the outlet port is occluded, a plurality of intermediate positions distal from the outlet port and an open position corresponding to the maximum opening of the outlet port (121, 122, 123); ii) a regulation member operatively connected with the shutter elements (221, 222, 223), which extends along a main axis (X-X) and is rotatable about said main axis (X-X), in such a way that one of its respective angular positions corresponds to a predefined position of the shutter elements (221, 222, 223) and thus to a regulation of the quantity of cooling liquid towards a respective duct of the cooling system; i) at least two shutter elements (221, 222, 223) operating with the respective outlet port (121, 122, 123), wherein each shutter element (221, 222, 223) is movable in an axial direction substantially orthogonal to the respective outlet port (121, 122, 123) between a closed position, in which the outlet port is occluded, a plurality of intermediate positions distal from the outlet port and an open position corresponding to the maximum opening of the outlet port (121, 122, 123); ii) a regulation member operatively connected with the shutter elements (221, 222, 223), which extends along a main axis (X-X) and is rotatable about said main axis (X-X), in such a way that one of its respective angular positions corresponds to a predefined position of the shutter elements (221, 222, 223) and thus to a regulation of the quantity of cooling liquid towards a respective duct of the cooling system;