Various fan models (Audi A4 B5)

The radiator fan - if it is not sufficiently supplied with oncoming air flow - must itself create a constant air flow in the radiator fins. The air absorbs the heat given off by the radiator. The more air passes through the plates, the better the heat is removed.

The Audi A4 is equipped with a serial so-called viscous fan. Vehicles only with «enhanced cooling» (e.g. with automatic transmission, trailer clutch, air conditioning) may be equipped with one additional or two, exclusively electrically driven, radiator fans.