Cooling System: Description and Operation

COOLING SYSTEM GENERAL

- The engine cooling system consists of a down-flow radiator which features high heat-dissipation performance, an electric-motor-driven fan, a water pump, a thermostat, and an engine coolant temperature sensor.

- The reservoir tank is made of translucent resin and enables easy confirmation of the coolant level. Also, coolant should be added to the reservoir tank when replenishment is necessary.

- The ECM controls the operation of the radiator main fan and sub fan depending on the signals from the engine coolant temperature sensor, vehicle speed sensor and A/C switch.


COOLING CIRCUITS

2. Cooling Circuits
The cooling system operates in three different phases depending on the temperature of the engine coolant.

- 1st phase (thermostat closed)
When the engine coolant temperature is below 76C (169F), the thermostat remains closed. The coolant flows through the bypass and heater circuits. This permits the engine to warm up quickly.

- 2nd phase (thermostat open)
When the engine coolant temperature is above 76 � 80C (169 � 176F), the thermostat opens. The coolant flows through the radiator where it is cooled.

- 3rd phase (thermostat open and radiator fan operating)
When the engine coolant temperature sensor sends a signal indicating a temperature above 95C (203F) to the ECM, it causes the radiator fan (or fans) to operate. When the engine is stopped after high-speed operation, vapor produced in the turbocharger cooling section flows from the coolant filler tank to the reservoir tank where it condenses back into water. Water is then absorbed by the coolant filler tank as the engine cools down.




COOLING
WATER PUMP
3. Water Pump
The water pump is located in the front portion of the left bank cylinder block and is driven by the engine through the timing belt. The thermostat is fitted into the coolant inlet at the bottom of the water pump. When the pump impeller rotates, the coolant is drawn into the pump from the lower pipe(which is connected to the radiator hose) via the thermostat. It then flows along the perimeter of the impeller and then is discharged for circulation through a circuit depending on the coolant temperature.





COOLING
MECHANICAL SEAL
4. Mechanical Seal
The mechanical seal has its seat tightly fitted on the water pump shaft. Since it is a hermetic seal forming an integral part of the water pump, the water pump cannot be disassembled.





COOLING
THERMOSTAT
5. Thermostat
The thermostat has a totally-enclosed wax pellet which expands as the coolant temperature increases. It opens and closes accurately at the preset temperatures and features high durability.






COOLING
RADIATOR FAN
A: DESCRIPTION
Each radiator fan is made of plastic. It is driven by an electric motor which is retained on a shroud.



COOLING
RADIATOR FAN





COOLING
RADIATOR FAN
B: FUNCTION
To reduce fan noise, the electric radiator fan control switches the fan speed to Low or High in accordance with the ECM's decision based on conditions such as engine coolant temperature, vehicle speed, and A/C load signals.

To switch the fan speed to Low or High, the circuit connects two motors in series (Low speed) or parallel (High speed).






COOLING
RADIATOR CAP
7. Radiator Cap
The radiator cap at the coolant filler tank side has a pressure valve and a vacuum valve. When the radiator inner pressure becomes higher than specified, the pressure valve opens to send coolant to the reservoir tank. Also, when the radiator inner pressure becomes lower than the atmospheric pressure during the cooling down phase, the vacuum valve opens to send back coolant from the reservoir tank to the radiator. These functions prevent damage to the radiator components.





COOLING
RELIEF VALVE CAP
8. Relief Valve Cap
The relief valve cap at the radiator side has a pressure valve. When the radiator inner pressure becomes higher than specified, the pressure valve opens to send coolant to the reservoir tank. This function prevents damage to the radiator components.

CAUTION: Due to the difference in construction, the relief valve cap cannot be used in place of the radiator cap at the coolant filler tank side. If the relief valve cap is fit on the coolant filler tank, overheating may occur.