Engine Cooling System - Mechanism & Function (H4DO): Other Subaru Outback BR

General

1. The engine cooling system consists of a down-flow radiator featuring 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 lower than the preset value, 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 reaches the preset value, 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 becomes higher than the preset value, the ECM receives a signal from the engine coolant temperature sensor and causes the radiator fan(s) to operate.

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

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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 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.

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Radiator Cap

The radiator cap 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 7