Engine Cooling System (H4SO) - Mechanism & Function: Other Subaru Outback BP

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.

Scheme 193

1. 1st phase (thermostat closed) When the engine coolant temperature is below 76°C (169°F), the thermostat remains closed. The coolant flows through the bypass and heater circuits. This permits the engine to warm up quickly.
2. 2nd phase (thermostat open) When the engine coolant temperature is above 76 - 80°C (169 - 176°F), 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 sends a signal indicating a temperature above 95°C (203°F) to the ECM, it causes the radiator fan (or fans) to operate.

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.

Scheme 194

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 195

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 196

MODELS WITH A/C

ENGINE COOLANT TEMPERATURE SPECIFICATIONS CHART (MODELS WITH A/C)

MODELS WITHOUT A/C

ENGINE COOLANT TEMPERATURE SPECIFICATIONS CHART (MODELS WITHOUT A/C)