I have heard that they should be changed every year or every other year. What dictates how often they should be changed? I know they need to be changed prior to the beginning of the season, but just wondered if they need to be changed after setting for the long winter every year? Have always changed every other year in the past, but have seen the condition that some of them are in. Thanks.

They should be changed every year in the spring before you use the boat for the first time, especially if you store the boat in a place that is not climate controlled. When the temperature changes from hot to cold, the impeller expands and contracts. It is dry while it is expanding and contracting and it has tendency to crack. The first time or two that you use the boat, those cracks can expand and the vains will break off of the impeller. Once a vain breaks, the whole impeller usually comes apart. It is cheap insurance in my eyes. Not to mention, it is a whole lot easier to take out the impeller in one piece, rather than in 50 pieces. Hope this helps, Eddie.