An engine system may include a thermostat casing connected to a first, second, third, and fourth flow channels, a valve guide in which a main valve that opens and closes the first flow channel is formed at one side, a closing valve that opens and closes the second flow channel is formed at the other side, and a bypass valve is formed adjacent to the closing valve, an elastic member that elastically supports the valve guide to enable the main valve to block the first flow channel and the closing valve to block the second flow channel, a driver that moves the valve guide so that the main valve opens the first flow channel and the closing valve opens the second flow channel according to a temperature of a coolant, and a control unit that controls the temperature and a flow of the coolant by controlling the driver.