Fan and thermostat question.

[sharpe1]

Hi guys, sorry if this is a repeat, but I have looked and can't find the answer in the FAQ's.
Does anyone know what the second thermofan is for and when it works? I've heard conflicting stories on how to change the thermostat on the alloytec V6, can someone give me the facts, thanks.

[Surfwagon]

Although mines a V8 my second fan (the smaller one) operates at all times the AC (climate control) is on whether the car is hot or cold.
My old VS which also had climate AC and only the "1" large fan had the fan running continuously at low speed when ever the AC was on.

[Luke52]

Conditions for Stage 1 Fan Operation

1 The Engine Cooling Fan Relay 1 is turned ON when :

- Air Conditioning request indicated (YES) and the vehicle speed is less than 30 km/h
-Air Conditoning pressure is greater then 1 500kPa (so no, it wont turn on just because the AC is on unless the pressure is above 1 500kPa)
-Coolantg temperature is greater than 104 C OR
-An engine coolant temperature sensor failure is detected by the PCM OR
-When the ignition switch is turned from ON to OFF and the engine coolant temperature sensor is above 117Cm the ECM will continue to engergise tyhe Engine Cooling Fan Relay 1 (R7) for approximately four minutes

2 The ECM switches OFF Enging Cooling Fan Relay 1 when the following conditons have been met:

-Air Conditioning request not indicated (NO) and the coolant temperature is less than 99C OR
-Air conditoning request indicated (YES) with pressure less than 1 700kPa, vehcile speed greater than 50 KMh and coolant temperature less than 99 C

Conditons for Stage 2 Fan Operation

The ECM determines when to enable the Engine Cooling Fan Relay 2 based on inputs from the ECT sensor

1 Engine Cooling Fan Relay 2 is turned ON if the Engine Cooling Fan Relay 1 has been energises for one second and the following conditions have been met:

-if there is a ECM message response fault, setting DTC P1258
-an ECT sensor failure is detected by the ECM.
-Engine coolant temperature is above 108C OR
-Air conditioning pressure is greater than 2 000kPa

2 If Stage 2 has been enabled, the ECM reverts to Stage 1 operation when:

-The Engine Coolant Temperature is less than 103C and
Air conditoning request not indicated (NO) OR
Air conditoning request indicated (YES) and the pressure is less than 1500kPA

Courtesy of Torquative from my thread a few months back.

So basically, the second fan is really only a back-up and kicks in if the engine is getting really hot, the first fan fails, or the A/C needs an extra kick.

[sharpe1]

Thanks Luke, that's awesome.