Originally Posted by Faster
There's a good chance your impeller is somewhat damaged.. they don't like to run dry. They will often continue to move adequate amounts of water despite a broken vane if there's no resulting pluggage... Also suddenly flashing cold water into an overheated block is another way to cause cracking.. probably better off the shut down, allow to cool then open the valve and restart.
Frequency of impeller changes probably should be based on hours more than simple elapsed time, but I know many who do it seasonally just because.
If part of an impeller vane is broken off it will find its way into the heat exchanger (if FWC) or 'who knows where' in the water jackets of a RWC engine. In a H/E it's usually easy to find/flush out. If it gets jammed up inside the engine itself it's very hard to know where it ended up and a passage could be 'starved' at some point. Not a nice prospect.
btw.. some people hang their engine key on the RW through hull valve handle.. tends to discourage 'forgetting'...
By leaving the raw water seacock closed will the impeller actually run dry? The way my engine is set up the engine is below the water line. So when the seacock is closed, the water pump is flooded. Now when the pump starts, it cannot get a suction of water, but is the pump still flooded with water? I am not sure how it would go dry as that would mean their would need to be a total vacuum at the pump.
I will plan to replace the impeller just a precaution in any event. That would be bad if pieces start breaking off.