Originally Posted by casey1999
A couple times I forgot to open the raw water engine cooling seacock after starting the engine. While warming up the engine the overheat alarm went off, opened the seacock and engine cooled down fine. It is raw water cooled so high temp alarm is at about 170 degree- should not have damaged engine.
I did not inspect the raw water pump and since then have run many hours on the engine without pump problems. Could the impeller still be damaged? I plant to change it say every 3 years.
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'...