Engine cooling system having a coolant control valve unit

An engine cooling system comprising:

• a cylinder block having one side for receiving a coolant, the coolant in the cylinder block flowing from the one side to an opposite side;
• a cylinder head disposed on the cylinder block and having one side and an opposite side for discharging coolant, the coolant in the cylinder head flowing toward the opposite side;
• a coolant pump configured to supply the coolant only to the one side of the cylinder block:
• a coolant control valve unit configured to continuously receive the coolant from the opposite side of the cylinder head and to supply the coolant to an oil cooler, a heater, and a radiator;
• and
• a control unit configured to determine a heating priority mode according to operation conditions,
• wherein the cylinder head receives the coolant only through the cylinder block,
• wherein the coolant circulated through the cylinder head is discharged from the opposite side of the cylinder head to the coolant control valve unit and the coolant circulated through the cylinder block is flowed into the cylinder head and is then discharged from the opposite side of the cylinder head to the coolant control valve unit,
• wherein the coolant control valve unit continuously receives the coolant circulated through the cylinder head, continuously supplies the coolant to the oil cooler, selectively supplies the coolant to the heater through a first coolant passage, selectively supplies the coolant to the radiator through a second coolant passage, and selectively receives the coolant passing the cylinder block through a third coolant passage, and
• wherein the control unit controls the coolant control valve unit to fully open the first coolant passage for the heater, to close the second coolant passage for the radiator, and to close the third coolant passage for the cylinder block or to control an opening rate of the third coolant passage in the heating priority mode.