Abstract: An engine cooling system for increasing and controlling a wall temperature of a cylinder head is provided. The cooling system includes a radiator passage that passes through a radiator, a radiator-bypass passage that bypasses the radiator, a first fluid temperature sensor that acquires a fluid temperature of an engine coolant flowing through a bore passage for cooling a cylinder, a second fluid temperature sensor that acquires the fluid temperature of the engine coolant flowing through a head passage for cooling a cylinder head, a thermostat valve arranged in the radiator passage, a flow rate regulator valve arranged in the radiator-bypass passage, and an electronic control unit (ECU). While controlling the thermostat valve on the basis of a detection result of the first fluid temperature sensor, the ECU controls the flow rate regulator valve on the basis of a detection result of the second fluid temperature sensor.