Patent ID: 8118001

Claim:
In a water-cooled internal combustion engine of the type including a coolant flow circuit for circulating coolant used to cool the internal combustion engine, said coolant flow circuit including a water jacket formed in the internal combustion engine and comprising a plurality of coolant flow passages which are communicably connected with each other for allowing flow of the coolant, a water pump for discharging coolant to the water jacket for cooling the internal combustion engine using the coolant, a radiator which cools the coolant, an oil cooler for cooling a lubrication oil using the coolant received from the water pump, a coolant overflow passage operatively connected with the coolant flow circuit, a reservoir tank operatively connected with said coolant overflow passage, the reservoir tank arranged to store the coolant received via the coolant overflow passage, and a pressure regulating valve interposed in the coolant flow circuit and operatively connected with the reservoir tank via said coolant overflow passage, wherein said pressure regulating valve discharges the coolant from the coolant flow circuit to the reservoir tank via the coolant overflow passage when pressure of the coolant in the coolant flow circuit reaches a predetermined value; the improvement comprising a coolant return passage for supplying coolant to the coolant flow circuit from the reservoir tank, said coolant return passage having a check valve interposed therein, wherein said coolant return passage is branched off from the coolant overflow passage; and wherein said coolant return passage is connected with the coolant flow circuit such that the coolant flows in one direction via said check valve from the reservoir tank to the coolant flow circuit.