Multi-purpose hydraulic system for a motor vehicle, said system comprising a primary hydraulic circuit, a secondary hydraulic circuit and a diverter valve, the primary hydraulic circuit comprising a primary hydraulic pump, and at least one primary using device communicating with a delivery duct of the primary hydraulic pump, the secondary hydraulic circuit comprising an electrically actuated secondary hydraulic pump and at least one secondary using device communicating with a delivery duct of the secondary hydraulic pump, wherein the diverter valve is applied to the delivery duct of the secondary hydraulic pump and is configured to selectively and alternately connect the delivery duct of the secondary hydraulic pump to the at least one secondary using device or to the at least one primary using device depending on the operation status of the primary hydraulic pump, wherein the diverter valve is an automatic hydraulic valve configured to open towards the at least one secondary using device - when the primary hydraulic pump is being operated - by means of the hydraulic pressure generated by the primary hydraulic pump within the primary hydraulic circuit, characterized in that said primary hydraulic circuit comprises an internal combustion engine, in that said at least one primary using device is a lubrication circuit for the internal combustion engine, in that the primary hydraulic pump is mechanically actuated by the internal combustion engine, and in that said at least one secondary using device is an oil jet cooling system, wherein the secondary hydraulic pump feeds the secondary hydraulic circuit arranged to cool the pistons of the internal combustion engine, by means of said oil jet cooling system, when the internal combustion engine is in operation, and feeds the primary hydraulic circuit when the internal combustion engine is inactive in said motor vehicle provided with a start-stop system or with a "sailing" function, so as to prevent wear of parts of the said internal combustion engine upon restarting thereof. wherein the diverter valve is an automatic hydraulic valve configured to open towards the at least one secondary using device - when the primary hydraulic pump is being operated - by means of the hydraulic pressure generated by the primary hydraulic pump within the primary hydraulic circuit, characterized in that said primary hydraulic circuit comprises an internal combustion engine, in that said at least one primary using device is a lubrication circuit for the internal combustion engine, in that the primary hydraulic pump is mechanically actuated by the internal combustion engine, and in that said at least one secondary using device is an oil jet cooling system, wherein the secondary hydraulic pump feeds the secondary hydraulic circuit arranged to cool the pistons of the internal combustion engine, by means of said oil jet cooling system, when the internal combustion engine is in operation, and feeds the primary hydraulic circuit when the internal combustion engine is inactive in said motor vehicle provided with a start-stop system or with a "sailing" function, so as to prevent wear of parts of the said internal combustion engine upon restarting thereof.