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Originally Posted by CJ_Boxster
Do the radiator fans in the front of the car turn on when the car reaches a certain temp or do they only turn on when the AC is turned on?
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Hi,
The Radiator Cooling Fans have two different speeds and are controlled by the DME. The operation of the Fans, or the selection of the Fan speed, is not temperature dependent alone. The DME uses several other variables to determine the Fans operation.
These include: Ambient Temperature (determined by Intake temperature from the integral Temperature Sensor in the MAF), Driving Speed (from the Wheel Speed Sensors, to judge the airflow through the radiators - another reason why keeping the Radiators clean is important), Engine Speed (to judge the vol./time of the Coolant flow - Coolant Pump flow is rpm dependent), Immobilization time since "Ignition OFF" (to judge heat buildup), AC Refrigerant Pressure (from the AC Pressure Switch, to judge load placed on Engine, affecting Engine Speed, especially at idle).
So, you cannot judge the proper operation of the Fans by the Temperature Gauge alone. In one instance, at one displayed temperature, the Fans may operate, or may operate on either High or Low. In another instance, with the same temperature displayed, the Fans may not operate at all, or may operate at a different speed.
For example, at idle, say at a Stoplight, the Fans may operate on High speed at Coolant Temperature
X, while at 65MPH, at that same Coolant Temperature
X, the Fans may operate at Low speed, or may not operate at all. There is a Temperature Default in the DME software which will override the other variables given the following conditions:
The Fans will
always work on Low speed: When the AC is switched ON, or if the Coolant Temperature exceeds 96.75°C (206.2°F).
The Fans will
always work on High speed: If the Coolant Temperature exceeds 102°C (215.6°F), or the AC Pressure Switch is CLOSED (when Refrigerant Pressure exceeds 16 bar or 232 PSI).
The caveat here is that the Fans may indeed work in the Default Mode, but due to a failed or failing Switch or Sensor, may not work optimally under normal driving conditions. This may account for some of the varying operating Coolant Temperatures some owners report having, but there are so many variables involved, that it's impossible to say for sure.
Hope this helps...
Happy Motoring!... Jim'99