I have a 1998 Mini Monza and not every time but pretty often my radiator fan comes on as soon as I start up. The temperature sensor on the thermostat appears to be functioning correctly - it Ohms out at 1.8kOhm when cool and 330Ohm when hot. I suspect its a MEMS issue but if anyone can shed light on this situation I'd very much appreciate it.

UPDATE: I found that Rover released a bulletin 0043 about this problem, which was related to a loose connection between the thermister sensor and the plug connector. It turns out mine were replaced with the parts to resolve the issue but I guess over time these parts suffer the same issues as those replaced.

I cleaned the contacts and the problem went away .... for now!