An engine system is provided, including an engine having a water jacket, a circulation system that circulates coolant through the water jacket, and a controller. The circulation system includes a radiator passage including a heat exchanger, a bypass passage bypassing the heat exchanger, a flow rate control device, and a thermally-actuated valve connected to the radiator passage and that opens to allow the coolant to pass through the heat exchanger. When an engine load is below a first load, the controller controls the flow rate control device to adjust the coolant flow rate flowing through the water jacket according to the load, by closing the radiator passage and adjusting the coolant flow rate flowing through the bypass passage. When the load is above the first load, the controller controls the flow rate control device so that the coolant flows through each of the radiator passage and the bypass passage.