Coolant Flow

This cooling system operates in 3 steps, depending on temperature of the coolant that is flowing through the cooling circuit. See Fig 1 .

1. Thermostat Closed
   
   When coolant temperature is below 169°F (76°C), the thermostat remains closed and the coolant flows through the bypass and heater circuits. This permits the engine to quickly warm up.
2. Thermostat Opened
   
   When coolant temperature is above 169-176°F (76-80°C), the thermostat opens and the coolant flows through the radiator where it is cooled.
3. Radiator Fan Operating
   
   When coolant temperature rises above 203°F(95°C), the ECM receives a signal from the engine coolant temperature sensor. The ECM then sends an ON signal to the radiator fan to rotate.

Fig 1: Identifying Engine Coolant Flow Pattern (2.2L Engine)

Courtesy of SUBARU OF AMERICA, INC.

Fig 2: Identifying Engine Coolant Flow Pattern (2.5L Engine)

Courtesy of SUBARU OF AMERICA, INC.