I have the Polo 1.1l rad, basically as small as they get. The fan only comes on after ~15 mins of idling in warm weather, or when stopping from a spirited ride. I hung the fan on zip ties through the core, but stuck some window sealer foam tape on the edge. The fan's efficiency is completely fine, it always goes back off within 30 seconds of turning on. I was stuck in traffic in 25°C heat on a couple of occasions, no cooling problems to report.
