[Steve Tinker]

Your biggest problem now is the plastic debris lodged in the cooling passageways of the cylinder heads. Some of the passages are small and if they get blocked or even partially obstructed by the remnants of your impeller, it causes localised overheating of the head. Not a good thing!!

Remove the thermostat and see if there is any debris in the housing and try and back flush the cooling system. I don't know how easy that is going to be, use the search function above to get more details. Perhaps JFPinPA, Jake Raby or someone who has already back flushed or cleaned out the cooling system can give you some tips.....