Customers usually ask what would happen to a fan if storage/operating temperatures go beyond advertised range.
At high storage/operating temperatures, there will be an increased rate of bearing grease evaporation. This will lead to reduction in life of the fan. At low storage/operating temperatures, the fan magnets will be demagnetized and lose its function to properly rotate the impeller.
Below -20C, some electronics might not work as expected which will lead to premature failures. Around -40C is where we expect immediate failures.
Sanyo Denki has a Wide Temperature fan series that is guaranteed to operate from -40°C to +85°C.