I have a bravo and replace the impeller every other year. Doing an alpha for someone. It has 3 years on it and looks great. Is change interval longer on an alpha? Do they last longer because they are in the lower and submerged before starting?

3 years is what Merc suggests unless you suck up sand or something like that. They don't last longer IMO, just a bigger PITA to change. You really want to change the impeller out while it still looks good. If it doesn't then it turns into a research mission to find missing pieces.

The Alpha Gen 1 didn't last as long as the Gen 2. The Gen 2 has made it easy for 5 years but I would still do it 3

My Verado's list every 3

I replace all my impellers yearly, despite only putting 10-20 hours on my stuff. Most of the time my impellers look perfect but I’ve seen a few look a bit more worn.

it’s an hours worth of work on the big boat and like 30 minutes on each of the O/B boats. Total cost is minimal. Certainly overkill, but just part of my winter maintenance process….

My brother never changed the impeller once in 15 years and ~500 hours on his 350 Magnum Alpha One...but it was run 100% in the clear, pure waters of Table Rock Lake, which I am sure had a positive effect on the life of it.

I know of a guy who bought his boat new in 1986, and didn't change his impeller til 2020. he installed an hour meter when he bought the boat and was over 1000 hours on the original impeller. Still was pumping water fine and not broke when he changed it, but he used his boat every single year, and in fresh water. It was an alpha 1, gen 1 behind a 350 chevy.

Grand dad always said "first liar doesn't stand a chance"

Just replaced mine this week. Pretty simple job. The one that came out looked like new but cheap maintenance.