Final answer:
Keeping the window washer reservoir full during the winter months is not advisable as the fluid can freeze and cause damage to the system.
Step-by-step explanation:
Keeping the window washer reservoir full during the winter months is not a good idea because the fluid can freeze. When the temperature drops below freezing, the water in the reservoir can turn into ice, which can cause damage to the fluid lines and nozzles. This can result in a malfunctioning window washer system.