Water pump impellers used for engine cooling are made of flexible material and they are a regular maintenance item. Impellers fail by breaking; the outer edges usually rip. Wear happens from age, use or abuse(such as starting an inboard or outboard engine out of water without a flushing device).
These items can fail very rapidly and without warning, causing an overheated engine and a bad day on the water.Signs of trouble may include lower water pressure and higher engine temperatures. The pieces coming off the impeller can end up inside the small water passages in your motor. Leftover parts of an impeller can cause overheating if they are not found and removed.
Engines are very expensive and take time to rebuild or replace. An impeller replacement is not very expensive or time consuming. When is the last time yours was replaced?