This just happened to me on my Z3. While attempting to change the thermostat, I turned on the car, and the fan exploded. Luckily for me, the hood was up so a blade ended up taking out just a grill (and my radiator and belts :roll eye )
So now I'm looking for a conversion to a electric fan. I've seen people remove all the fan (aux and clutch) and run a powerful SPAL puller fan on the factory Aux harness.