An engine system includes a cylinder block and a cylinder head. A coolant control valve unit is engaged with the cylinder head to receive a coolant exhausted from the cylinder block and a coolant exhausted from the cylinder head. The coolant control valve unit controls a coolant to be supplied to a heater, a radiator, and an oil cooler and controls the coolant exhausted from the cylinder block. The coolant control valve unit receives the coolant from the cylinder head, supplies the coolant to the oil cooler, and controls the coolant distributed to the heater and the coolant exhausted from the cylinder block.