Engine Cooling System - Mechanism & Function (H4DOTC): Other Subaru Outback BR рестайлинг

General

1. 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.
2. 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.
3. 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

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

1. 1st phase (thermostat closed) When the engine coolant temperature is below the preset temperature, the thermostat remains closed. The coolant flows through the heater circuit. This permits the engine to warm up quickly.
2. 2nd phase (thermostat open) When the engine coolant temperature becomes higher than the preset temperature, the thermostat opens. The coolant flows through the radiator where it is cooled.
3. 3rd phase (thermostat open and radiator fan operating)

When the engine coolant temperature sensor bocomes hotter than the preset value, the ECM receives signals from the engine coolant temperature sensor and causes the radiator fan(s) 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.

Note. Refer to the Service Manual for preset engine coolant temperature values for each stage.

Scheme 10

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's 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.

Scheme 11

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.

Scheme 12

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.

Scheme 13

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.

Scheme 14

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.

Scheme 15