ENGINE COOLING SYSTEM

PROBLEM TO BE SOLVED: To provide an engine cooling system that promptly eliminates deterioration in fuel consumption due to friction loss in the cold state while securing cooling performance for auxiliary machines by a simple configuration.SOLUTION: The engine cooling system includes: a bypass passage 17 for internally circulating cooling water in a water jacket 8; an auxiliary passage 20 that communicates between the upstream side and the downstream side of a water pump 10 and circulates cooling water supplied to auxiliary machines; and an electromagnetic valve 19 for opening/closing the bypass passage 17. When there is no local abnormal rise in the temperature in an engine body 5 in the cold state, the internal circulation of cooling water in the water jacket 8 is inhibited in order to efficiently accelerate warming-up of the engine body. On the other hand, when there is an abnormal local rise in the temperature in the engine body 5 in the cold state, cooling water in the water jacket 8 is internally circulated in order to smooth the temperature in the engine body 5, thereby also coping with heat damage or the like to the engine body 5.