Audi a3 why does my radiator fan keep running even when its cold on my audi a3 2005

Waterpump has plastic impeller prone to breaking also check thermostat

Hi I have the same problem which fan is the air con fan on the a3 is it the small one or large one?

Fan not working, thermostat not opening, dirty radiator inside or outside. Faulty sensor.

You may need to reset basic settings for the control module using a scan tool , reading the logged faults stored in the control module is needeed also .

There is a fan switch,,,,sometimes called a sensor which controls the fan....usually located on the back side of the radiator....likely on the left side....about halfway between top and bottom...replace it...Must drain radiator down to that point...Joe LittleBear

you could check the temp/fan sensor.but when you say cold do you mean first start of day??cos if the head has hot water in it over a set temp then the fan will start but will go off when cooler.stops hotspots...

are you installing the thermostat correctly? the correct direction? how can the radiator be blocked if ok when the thermostat is removed?

If you have no radiator cap that can be removed, you will probably have to do repeated cycles of engine temperature and just add coolant to the overflow until the engine stops draining it. This isn't like a hydraulic (brake) system so the chance of leaving bubbles behind is far less.
With a radiator cap, it's pretty simple; run the engine until the coolant is visibly circulating and add coolant as the level drops.

If your cooling fan is not working you solved your own problem. The cooling fan is what helps your radiator perform its function. The radiator cools down the antifreeze mixture by separating it into small tubes separated by air fins, the fins allow a greater surface area for air. The radiators main function is to dissipate heat into the surrounding atmosphere which it can do well at highway speeds without a fan, but most modern cars need a cooling fan to help pull air across the radiator.
The wiring diagram for your vehicle suggests that there is a 5 amp fuse 4 and a 40 amp fuse 42 that run the radiator fan and control which should be located in an under hood fuse/relay box. Check them with a test light on both sides, with the light to ground you should see a positive voltage at both sides. the 40 amp would most likely be a maxi fuse, or a larger size then the regular atm fuse for the 5 amp,

yeah try to change the sensor.maybe it is busted. normally, most of the late-model cars comes with a fan feature that turns of after 5 or 10 mins even after switching off the engine. this helps to cool down first the engine to reach its desirable temperature before it is totally shut down. its good that your radiator fan has a feature like that. aftermarket perfomance fans do come with that feature because it takes care of the engine state.just try to change the sensor for engine temp