I'm pretty sure that the fan and water pump are controlled by the ECU. In my car, (r56 MCS) the fan and water pump kick into high gear (so to speak) at about 225F as read by a Scangauge 2 plugged into the OBD2 port, and when the AC is turned to max. I'm sure there are other parameters involved, but that's what I've noticed.
Sorry for the disturbance but just an additional to this thread. I actually went on a 26 mile round-trip and the cooling fan has stopped half-way where the fan usually comes on but had shift to journey Temp and the problem was gone. You can actually buy genuine mini parts on local stores or if you wish you could have them online with great deals and discounts.
I noticed these posts on the cooling fan and wondered how long does it take after starting a mini cooper (2008) for the fan to kick on? The reason I asked is that I changed out a leaky thermostat and after flushing the system I always let my cars idle and wait until the fan turns on. Just a check to make sure everything is ok. Well after 20 mimutes or so my fan still didn't turn on. I drove it around the block and still the fan was not on. So I turned the mini off and now I am wondering if something is wrong with my fan or a sensor.