An engine cooling system is provided, which includes a water jacket through which coolant flows, a heat exchanger that cools the coolant, a first bypass passage that bypasses the heat exchanger and recirculates the coolant to the water jacket, a radiator passage that recirculates the coolant to the water jacket via the heat exchanger, and a flow control device that is installed at a location where a coolant passage branches into the first bypass passage and the radiator passage and performs a water flow control to adjust a coolant amount flowing into the water jacket by adjusting a coolant amount flowing through the first bypass passage. A thermally-actuated valve connected with the radiator passage via a second bypass passage is provided to the first bypass passage, and when this valve opens, the coolant flowing through the first bypass passage flows into the radiator passage through the second bypass passage.