I have a 2002 crownline with 4.3 Merc/Alpha 1. It gave me an alarm the other night while coming back to the dock. I noticed the temp gauge was high and pulled it out of the water. I figured to change the impeller and see where to go from there. In the process of changing, I noticed that the plastic tube connecting the pump upper housing to the copper water tube had melted. The impeller was in good shape (changed it anyway) But I have no idea what caused it to melt, and what to do to fix it. Any help would be welcome.