Patent ID: 7484479

Claim:
A water-cooled internal combustion engine comprising: an engine body having: a cylinder block provided with a plurality of cylinders arranged in a cylinder arranging direction; a cylinder head joined to the cylinder block and provided with a plurality of combustion chambers respectively corresponding to the cylinders and with exhaust ports connected to combustion chambers, respectively; and a water pump for pumping cooling water; the cylinder block having a cylinder block water jacket formed therein and substantially surrounding the cylinders, the cylinder head being provided with a cylinder head water jacket formed therein and substantially surrounding the combustion chambers and the exhaust ports, and with an exhaust manifold passage into which exhaust gas flows from the combustion chambers through the exhaust ports, respectively: wherein the exhaust manifold passage is formed only in the cylinder head and has an exhaust gas outlet through which the exhaust gas collected in the exhaust manifold passage flows out from the cylinder head; and the exhaust manifold passage is surrounded by the cylinder head water jacket and a discharge water jacket, the discharge water jacket being formed in the cylinder head and connected to the cylinder block water jacket and the cylinder head water jacket in such a manner that cooling water from the cylinder block water jacket and the cylinder head water jacket is discharged to the outside of the engine body through the discharge water jacket; wherein the cylinder block water jacket communicates with the discharge water jacket by means of a cylinder block connecting passage in which a cylinder block thermostat valve is disposed; and wherein the cylinder head water jacket communicates with the discharge water jacket by means of a cylinder head connecting passage in which a cylinder head thermostat valve is disposed.