2006-2008 Subaru Tribeca Service & Repair Manual

2008 ENGINE Mechanism & Function - Cooling (H4SO) GENERAL  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.  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 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 lower than the preset value, the thermostat remains closed. The coolant flows through the heater circuit. This permits the engine to warm up quickly.  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.  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. 2008 Subaru Tribeca 2008 ENGINE Mechanism & Function - Cooling (H4SO) 2008 Subaru Tribeca 2008 ENGINE Mechanism & Function - Cooling (H4SO)

Fig. 1: Cooling Circuits Diagram Courtesy of SUBARU OF AMERICA, INC. WATER PUMP 2008 Subaru Tribeca 2008 ENGINE Mechanism & Function - Cooling (H4SO)

Fig. 2: Identifying Water Pump And Components Courtesy of SUBARU OF AMERICA, INC. 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. 2008 Subaru Tribeca 2008 ENGINE Mechanism & Function - Cooling (H4SO)

Fig. 3: Identifying Mechanical Seal Courtesy of SUBARU OF AMERICA, INC. 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. 2008 Subaru Tribeca 2008 ENGINE Mechanism & Function - Cooling (H4SO)

Fig. 4: Identifying Thermostat Courtesy of SUBARU OF AMERICA, INC. RADIATOR FAN DESCRIPTION Each radiator fan is made of plastic. It is driven by an electric motor, which is retained on a shroud. 2008 Subaru Tribeca 2008 ENGINE Mechanism & Function - Cooling (H4SO)

Fig. 5: Identifying Radiator Fan Assembly Courtesy of SUBARU OF AMERICA, INC. To reduce fan noise, the fan output is two-stepped and can be switched to Low or High according to the load on A/C, coolant temperature, and vehicle speed. This control is accomplished by a circuit as shown below; the output is changed by switching the connection of two motors between serial and parallel instead of using components such as resistors. 2008 Subaru Tribeca 2008 ENGINE Mechanism & Function - Cooling (H4SO)

Fig. 6: Radiator Fan Circuit Diagram Courtesy of SUBARU OF AMERICA, INC. FUNCTION On models equipped with an air conditioning system, the ECM receives signals from the engine coolant temperature sensor, vehicle speed sensor and A/C switch, and based on these signals, the ECU controls the fan speed to Hi or Low. Operation examples: VEHICLE SPEED SPECIFICATION Vehicle speed A/C compressor load Engine coolant temperature Rising: below 95°C (203°F) Lowering: below 92°C (198°F) Rising: between 96 and 99°C (205 and 210°F) Lowering: between 93 and 94°C (199 and 201°F) Rising: over 100°C (212°F) Lowering: over 95°C (203°F) Operation of Operation of radiator Operation of 2008 Subaru Tribeca 2008 ENGINE Mechanism & Function - Cooling (H4SO)

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. radiator fans fans radiator fans When accelerating: below 19 km/h (12 MPH) When decelerating: below 10 km/h (6 MPH) OFF OFF Low-Speed High-Speed Low Low-Speed Low-Speed High-Speed High High-Speed High-Speed High-Speed When accelerating: between 20 and 69 km/h (12 and 43 MPH) When decelerating: between 11 and 64 km/h (7 and 40 MPH) OFF OFF Low-Speed High-Speed Low High-Speed High-Speed High-Speed High High-Speed High-Speed High-Speed When accelerating: between 70 and 105 km/h (43 and 65 MPH) When decelerating: between 65 and 103 km/h (40 and 64 MPH) OFF OFF Low-Speed High-Speed Low OFF Low-Speed High-Speed High Low-Speed High-Speed High-Speed When accelerating: over 106 km/h (66 MPH) When decelerating: over 104 km/h (64.6 MPH) OFF OFF OFF High-Speed Low OFF Low-Speed High-Speed High OFF Low-Speed High-Speed 2008 Subaru Tribeca 2008 ENGINE Mechanism & Function - Cooling (H4SO)

Fig. 7: Identifying Radiator Cap Courtesy of SUBARU OF AMERICA, INC. 2008 Subaru Tribeca 2008 ENGINE Mechanism & Function - Cooling (H4SO)

2006-2008 Subaru Tribeca Service & Repair Manual

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