Re: Premature impeller failure cause
I think something other than the supply line possibly being a bit too small is going on. If the through hull, strainer and hose supplied the 46 OK I don't see why the impellers are falling apart on the new engine. You said the new impeller is smaller than the old one meaning that it's a smaller pump overall than the old pump. That doesn't make sense to me as they are sized according to gpm required and that would mean that the higher HP engine requires less cooling water than the old engine and if that is true then the through hull and hose should be more than adequate. I would talk directly to Westerbeke and confirm that you have the correct pump for that engine.
SV Laurie Anne
1988 Brewer 40 Pilothouse