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 through which the outbound cooling liquid flows; - a regulation chamber located between the inlet port and the outlet ports ; - regulation means housed in the regulation chamber comprising: i) at least two shutter elements operating with the respective outlet port , wherein each shutter element is movable in an axial direction substantially orthogonal to the respective outlet port 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 ; ii) a regulation member operatively connected with the shutter elements , 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 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 comprises a control end 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 through which the outbound cooling liquid flows; - a regulation chamber located between the inlet port and the outlet ports ; - regulation means housed in the regulation chamber comprising: i) at least two shutter elements operating with the respective outlet port , wherein each shutter element is movable in an axial direction substantially orthogonal to the respective outlet port 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 ; ii) a regulation member operatively connected with the shutter elements , 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 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 operating with the respective outlet port , wherein each shutter element is movable in an axial direction substantially orthogonal to the respective outlet port 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 ; ii) a regulation member operatively connected with the shutter elements , 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 and thus to a regulation of the quantity of cooling liquid towards a respective duct of the cooling system; <EOS>