225 HP impeller question

I have a 2004 225 HP Honda that this will be my third season owning. I'm not too mechanically inclined (can do oil changes, etc), so I'm having my dealer change out the impeller. They called and said they need a new housing for the impeller because it was somewhat melted. Not a big deal price wise, but am curious about how it may have happened. As I can best remember, I haven't started the motor out of the water. Is this something that I could have been running with for two seasons without a problem? How long does the motor need to be running out of water for this to have happened? Could it happen with the motor in water?

Thanks.

The impeller can actually wear the sides of the pump housing and lose efficiency, especially if you have run aground a few times and ingested mud or sand into the pump. I make it a habit to change out the entire pump, instead of just the impeller, every 400 hours. The cost is not much different - part more expensive, labor slightly cheaper.

Question is, why was the housing melted?

If it has always pumped water for you, then the damage was done before you owned it.

Install a complete pump. You should change the impeller every two years, whether you use the engine or not.