Originally Posted by gerberpollack
how does the impeller relate to the water pump? if the inspection noted that the water pump needed to be replaced, does this mean the water wasn't circulating? shouldn't they have told me not to run the boat until it was replaced? seems like a pretty big deal.
yes, there was a screaching, not too loud, when i ran the boat. this was the reason i asked them to check the blower (thinking it was the blower). would most mechanics diagnose the problem if they heard a screaching?
The impeller is the flexible rubber thing. It mounts on the shaft and inside the pump housing. The pump housing is mounted to the engine so it doesn't turn. When the engine rotates, the impeller inside the housing turns and that's how it pumps water. The pump shaft is therefore inside the pump housing and mounted in a bearing. If the bearing goes, the pump shaft can overheat, get scored and fracture. When a bearing is gone, you get that grating sound you mention. Most mechanics would be alarmed if they heard that sound. They may not ascribe it immediately to the water pump, but they ought to look for its source.
IMHO, a bad raw water pump should be detected on a pre-sale inspection. If the bearing is gone, then the seal is gone too, and it's likely the pump was leaking water. Now, I don't know over what time course this all happened, but as JimN said, the timing of your raw water pump going right after the sale is...odd.
They didn't tell you the pump needed to be replaced, they told you the impeller
needed to be replaced. The impeller is a $30 wear item and is supposed to be automatically replaced every year (according to Indmar) as part of annual maintenance. Maybe they thought that the reason the boat was overheating was that it had a bad impeller, when in reality the whole pump was about to land in the bilge. A new impeller is $30. A new pump is about $180 (comes with impeller IIRC).
I'd have a chat with the selling dealer. Removing and replacing a raw water pump isn't a difficult job for someone who knows how to do it, but I get the impression you've never done that before and you might be better off having a tech do it.