I've has mine Z for nearly three years and don't ever recall the fan coming on. I'm pretty sure I saw somewhere in an old post that the fan doesn't cut in till coolant gets to 105C!! I guess it then turns off again a good few degrees lower than this. If this is right(?) it suggests to me that leaving it idling till the fan comes on might mean you've got a long wait anyway, even if it is working!?

Kev would probably have the definitive on/off temperatures?