As an aside looked up the term Otter switch as it seems to be regularly banded about. Not much directly on Google, but found that early contenders for controlling electric rad fans when they came on the scene, were a company called Otter Controls, which still exists. It seems they grabbed the market, notably being used on E types. Inevitably I suppose there is the association with the mammal as both live in water
Regarding the thermostatic switch, ideally there needs to be a temperature spread of a few degrees between contacts closing and opening again to avoid the regular cycling of fan.
