A pump group of a cooling system of a vehicle engine, the pump group extending with respect to an axis (X-X) and comprising: - an impeller rotatable around the axis (X-X); - a shaft extending along the axis (X-X) comprising an impeller end on which the impeller is integrally mounted; - an electric motor comprising a rotor integrally mounted on the shaft and a stator which surrounds the rotor axially and circumferentially; - a pump body extending with respect to the axis (X-X) comprising: i) an impeller casing which houses the impeller in an impeller chamber; ii) a motor casing which houses the electric motor in a motor chamber, wherein the motor casing comprises an intermediate tubular wall which extends parallel to the axis (X-X) positioned in an intermediate radial position between the rotor and the stator, so that a rotor chamber and a stator chamber are defined in the motor casing; wherein the rotor chamber and the stator chamber are sealingly separated from each other; wherein said pump group is characterized in that the stator chamber contains a predefined amount of cooling oil which at least partially fills the stator chamber in a manner such as to cool the stator by convection, wherein the predetermined amount of cooling oil fills a part of the stator chamber defining a free surface, such that, with the pump group subject to shaking, for example due to the motion of the vehicle, the cooling oil is free to move in the stator chamber promoting a cooling of the stator by forced convection. - an impeller rotatable around the axis (X-X); - a shaft extending along the axis (X-X) comprising an impeller end on which the impeller is integrally mounted; - an electric motor comprising a rotor integrally mounted on the shaft and a stator which surrounds the rotor axially and circumferentially; - a pump body extending with respect to the axis (X-X) comprising: i) an impeller casing which houses the impeller in an impeller chamber; ii) a motor casing which houses the electric motor in a motor chamber, wherein the motor casing comprises an intermediate tubular wall which extends parallel to the axis (X-X) positioned in an intermediate radial position between the rotor and the stator, so that a rotor chamber and a stator chamber are defined in the motor casing; i) an impeller casing which houses the impeller in an impeller chamber; ii) a motor casing which houses the electric motor in a motor chamber, wherein the motor casing comprises an intermediate tubular wall which extends parallel to the axis (X-X) positioned in an intermediate radial position between the rotor and the stator, so that a rotor chamber and a stator chamber are defined in the motor casing; wherein the rotor chamber and the stator chamber are sealingly separated from each other; wherein said pump group is characterized in that the stator chamber contains a predefined amount of cooling oil which at least partially fills the stator chamber in a manner such as to cool the stator by convection, wherein the predetermined amount of cooling oil fills a part of the stator chamber defining a free surface, such that, with the pump group subject to shaking, for example due to the motion of the vehicle, the cooling oil is free to move in the stator chamber promoting a cooling of the stator by forced convection.