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.
Thanks for the ideas. The pump I have looks exactly like the standard pump in the manual drawings and the part # for the impeller that fits the pump is part of the standard part list and the spare part kit so I don't think I have the wrong pump. My understanding is that the standard pump turns at a greater speed than the pump on the old 46 hp.
My initial suggestion to my mechanic was to possibly go with a higher volume pump and at the same time configure the mount so that the impeller was more accessable. Right now you need to unbolt the pump to get to the impeller without working blind. The mechanic indicated that upgrading to a larger thru hull would be a cheaper option to try first. I'll see what Westerbeke suggests.