It appears more or less a simple mechanism: a plastic fan screwed to the metal BBQ grid, a sensor in line in the top rad hose (ie the hose coming from the rad has been cut and the sensor fitted between the two halves) and some wires sourcing power and ground somewhere.
The fan was in place when I bought the LR (IIA 88 2.25 diesel).
How can I test that it works? If I wanted to check a viscous fan I'd look at it! If I wanted to check the thermostat was working I'd remove it and drop it in a pot of hot water to see if it opened/closed, but these new-fangled (!) electric fans are beyond me and I'd prefer not to dismantle it.
The LR's temp guage sits above the midway point but the vehicle does not appear to overheat - I'm used to guages which remain stubbornly at the bottom end of their travel. After sitting in traffic for a while the guage climbs higher but the fan doesn't seem to kick in (i listened for it, then climbed out for a look-see).
Maybe I shouldn't fret about it but I'd like to know the thing was working before undertaking long journeys. Engine runs beautifully BTW and fuel consumption is unbelievable after coming from petrol Landies!