It’s tempting to ignore an engine cooling impeller on the admirable principle of, ‘If it ain’t bust, don’t fix it.’ Most rules can be proved by examining the exceptions, however, and this is one of them. Over the seasons, and especially during long winter lay-ups, impellers steadily harden so that performance drops off imperceptibly. Blades suffer minor damage, perhaps splitting over half their length, making them more likely to rip off if a blockage runs them dry for a minute or two.
Check the impeller at the beginning of the season. If it’s tired, replace it. If it looks good, at least you know that the screws on the end plate all work. When you need to change it in a hurry on a lee shore, you won’t lose your ship because of a stripped thread.