Water-cooled internal combustion engine

A water-cooled internal combustion engine (1), for equipping scooters and motorcycles, having:

• a monobloc engine block (2) with a crankshaft substantially perpendicular to a longitudinal development of the internal combustion engine;
• a cooling system comprising a radiator (8), a fan (9) related thereto and a water circulating pump (11), driven by said crankshaft, comprising an intake nozzle (12) and a discharge nozzle (13), the fan (9) directly fitted onto said crankshaft (3), interposed between the radiator and the engine block the fan (9) lying on a plane substantially parallel to said longitudinal development;
• and
• an electric motor operated as a starter motor and as a current generator, arranged between the fan and the engine block and comprising a rotor fitted onto said crankshaft,
• said cooling system further comprises:
• a first cooling circuit having:
• a discharge line (16) and a extraction line (17) connecting the radiator (8) to said engine block (2), said discharge and extraction lines (16, 17) being constituted by tubes outside the engine block (2) with respective discharge openings (18), formed in said engine block (18), and intake opening (23) connected to said intake nozzle (12) of the pump (11);
• an inner circuit portion (24, 25) for extracting heat from the engine;
• a second cooling circuit wholly included in said engine block (2) for recirculating cooling water, comprising a by-pass line (26), connecting said discharge opening (18) to the intake nozzle (12) of the pump (11), and said inner circuit portion (24, 25) for extracting the heat from the engine (1);
• and
• a by-pass valve (27), arranged on the engine block (2) at said discharge opening (18), actuated by a thermostat (29) sensible to the water temperature, allowing the water circulation either in said first cooling circuit, above a reference temperature, or in said second cooling circuit, below said reference temperature.