Over the past several days I noticed the heater wouldn't work unless I rev the crap out the engine. I went on a troubleshooting rampage and made sure nothing was blocked in the system. I even cranked it with the inlet line from the radiator in a bucket of water. After I changed the thermostat, put it all back together and see the same thing happening.

The radiator inlet hose is nearly too hot to touch and the radiator outlet hose is ambient temperature. The heater barely has any heat at all and it won't take anymore water.

I haven't noticed any severe corrosion on the coolant plumbing so I have a hard time thinking that part of the impeller came off. Anyone have any ideas?

 

Any ideas? There are no other symptoms. How often to water pump blades rust away?