Cooling system of an internal combustion engine (ICE) comprising a cooling circuit (CC) with - a pump (P) to circulate coolant, - a radiator (R) suitable to disperse heat produced by the internal combustion engine in the ambient, - at least a first pipe (P1) to convey coolant from the internal combustion engine towards the radiator and - at least a second pipe (P2) connecting the radiator with the pump, The system further comprising - a cylinder (C)/piston (P) assembly (CPA) defining a chamber (CH) suitable to be hydraulically connected with said second pipe (P2) though a third pipe (P3) communicating with said second pipe (P2), - an actuator (A) connected to said piston in order to control its displacement in said cylinder, by varying said chamber volume, - a pressure sensor (PR) in hydraulic communication with said cooling circuit (CC) and - an electronic control unit (ECU) coupled with said pressure sensor and with said actuator and configured to control said actuator in order to maintain a pressure measured by said pressure sensor above a predetermined threshold; the system being characterized in comprising a three-way valve (V1), wherein a first port of the three-way valve (V1) communicates with said cooling circuit, wherein said cylinder/piston assembly is connected to a second port of said three-way valve (V1), and wherein the system further comprising a coolant tank (T) connected with a third port of said three-way valve (V1); wherein according to a first condition a) the three-way valve connects the cylinder/piston assembly with said coolant tank, and according to a second condition b) the three-way valve connects the cylinder/piston assembly with the cooling circuit (CC) and wherein said control unit (ECU) is configured to control also said three-way valve so as the three-way valve is in said b) condition when the piston displacement is adjusted to maintain a pressure measured by said pressure sensor above said predetermined threshold. - a pump (P) to circulate coolant, - a radiator (R) suitable to disperse heat produced by the internal combustion engine in the ambient, - at least a first pipe (P1) to convey coolant from the internal combustion engine towards the radiator and - at least a second pipe (P2) connecting the radiator with the pump, The system further comprising - a cylinder (C)/piston (P) assembly (CPA) defining a chamber (CH) suitable to be hydraulically connected with said second pipe (P2) though a third pipe (P3) communicating with said second pipe (P2), - an actuator (A) connected to said piston in order to control its displacement in said cylinder, by varying said chamber volume, - a pressure sensor (PR) in hydraulic communication with said cooling circuit (CC) and - an electronic control unit (ECU) coupled with said pressure sensor and with said actuator and configured to control said actuator in order to maintain a pressure measured by said pressure sensor above a predetermined threshold; the system being characterized in comprising a three-way valve (V1), wherein a first port of the three-way valve (V1) communicates with said cooling circuit, wherein said cylinder/piston assembly is connected to a second port of said three-way valve (V1), and wherein the system further comprising a coolant tank (T) connected with a third port of said three-way valve (V1); wherein according to a first condition a) the three-way valve connects the cylinder/piston assembly with said coolant tank, and according to a second condition b) the three-way valve connects the cylinder/piston assembly with the cooling circuit (CC) and wherein said control unit (ECU) is configured to control also said three-way valve so as the three-way valve is in said b) condition when the piston displacement is adjusted to maintain a pressure measured by said pressure sensor above said predetermined threshold. <EOS>