Cooling water circulating system for internal combustion engine of vehicle

A coolant circulating system in a water-cooled internal combustion engine of a vehicle, said system comprising:

• a coolant circuit including a circulation pump for circulating coolant through the engine, the coolant circuit having a direction of circulation;
• a heat accumulation tank having a heat insulating structure for accumulating therein coolant flowing out from the engine;
• a heater core disposed on the downstream side of the heat accumulation tank for exchanging heat between the coolant flowing out from the heat accumulation tank and air for heating a compartment in the vehicle;
• heat exchanger means disposed in the coolant circuit on the downstream side of the heater core for exchanging heat between the coolant and at least one of the engine lubricating oil, the automatic transmission operating oil, and engine intake air;
• and
• a coolant circuit portion for connecting the heat exchanger means on the downstream side thereof to the inlet side of the engine.