The cooling situation is rather complicated. Refer to the excerpt below from the VF Workshop manual:
Thermostat
When the coolant temperature is below 86°C (186°F) for V8 and 82°C (180°F) for V6 the thermostat valve remains closed. This prevents circulation of the coolant to the radiator and allows the engine to warm up quickly. After the coolant temperature reaches 86°C (186°F) or 82°C (180° F) the thermostat valve will begin to open. The coolant is then allowed to circulate through the radiator where the engine heat is dissipated to the atmosphere. The thermostat also provides a restriction in the cooling system, even after it has opened. This restriction creates a pressure difference which prevents cavitation at the water pump and forces coolant to circulate through the engine block.
Cooling Fan Operation
The cooling fans operate in two stages for V8 and three stages for V6; in both low and high stages both fans run. In stage 1 (low) the two fan motors are connected in series so both fans run at low speed. In stage 2 (high) each fan motor is connected to battery voltage so both fans run at high speed, (cooling fan operation is controlled by the engine control module (ECM) based on inputs from the following:
- The A/C request signal
- The A/C refrigerant pressure sensor
- The engine coolant temperature (ECT) sensor
Low Speed - Both Fans Operate at Low Speed
When the conditions for low speed operation are met the ECM provides a ground to the coil of engine cooling fan relay 1, causing it to operate (turn ON). The fan current path is then from the battery via the left radiator fan fuse, through the left fan motor, cooling fan relay 2, the right fan motor and cooling fan relay 1 to ground. The conditions for low speed operation are:
- There is an A/C request and:
- A/C refrigerant pressure is greater than 1517 kPa (220 psi).
- ECT is greater than 109°C (228°F) for V6 or 104°C (219°F) V8.
- ECT is greater than 121°C (250°F) for V6 or 113°C (235°F) for V8 when the engine is switched off (in this case stage 1 will operate for approximately four minutes - this is referred to as low fan run-on).
Low speed operation will cease when:
- There is no A/C request and the ECT is less than 105°C (221°F) for V6 or 100°C (212°F) for V8.
- There is an A/C request and the A/C pressure is less than 1000 kPa (145 psi) and the ECT is less than 105°C (220°F) for V6 or 100°C (212°F) for V8.
Mid Speed - Left Fan Operates at High Speed (V6 Only)
When the conditions for mid speed operation are met the left fan gets battery voltage and operates at high speed. The right fan does not operate. The conditions for Mid Speed operation are:
- The A/C has been requested and the A/C pressure is greater than 1700 kPa (247psi).
- The ECT is greater than 112°C (234°F) for V6 .
Mid speed operation will cease and revert to low speed operation when:
- ECT is less than 108°C (226°F) and there is no A/C request.
- There is an A/C request and the A/C pressure is less than 1200 kPa (174psi) and the ECT is less than 108°C (226°F).
High Speed - Both Fans Operate at High Speed
When the conditions for high speed operation are met the ECM provides - in addition to that already provided for the coil of engine cooling fan relay 1 - a ground to the coils of engine cooling fan relays 2 and 3, causing them to operate (turn ON). For the left fan, the current path is then from the battery via the left radiator fan fuse, through the left fan motor and engine cooling fan relay 2 to ground. For the right fan, the current path is from the battery via the right radiator fan fuse, through engine cooling fan relay 3, through the right fan motor and engine cooling fan relay 1 to ground. The conditions for high speed operation are:
- The A/C has been requested and the A/C refrigerant pressure is greater than 2000 kPa (290 psi).
- The ECT is greater than 117.5°C (243°F) for V6 or 109°C (228°F) for V8.
- An ECT sensor fault is detected and a DTC is set.
- There is a body control module (BCM) message response fault, which will cause a powertrain interface module (PIM) DTC to set.
If low speed operation is off when the conditions for high speed operation are met, high speed operation will be initiated five seconds after initiation of low speed operation.
High speed operation will cease and revert to low or medium speed operation when:
- The ECT is less than 112°C (235°F) for V6 or 103°C (217°F) for V8 and there is no A/C request.
- There is an A/C request and the A/C refrigerant pressure is less than 1400 kPa (203 psi) and ECT is less than 112°C (235°F) for V6 or 103°C (217°F) for V8.
