Times not always on your side

The importance of regular maintenance can never be stressed enough. The owners manual usually spells out just what exactly one should do to prevent premature failure.
  As we move into a new century, many of us have taken  these procedures for granted, often ignoring the dangers of those actions. We depend on lights and buzzers to tell us that it's time to pay attention to our cars, boats, and other machinery. But unfortunately, the warning device doesn't always work as designed by the manufacturer.  There may be circumstances under which a damaging situation can arise, and the warning lights and buzzers don't activate. Although we'd all love to blame the manufacturer, and some blame does lie there, the truth is that we need to ask ourselves,  did we do all we could do to prevent damage to our engine or boat.
The answer  to that question can best be answered by one good example. The manufacturer for brand XYZ, produces a product that recommends that the water pump impeller be replaced every season. Brand XYZ recently improved their design for a certain water pump model, claiming the benefits of it's new design. The older model pump, (in production for over twenty years) had an intolerance to running dry but contrary to the recommended service interval, typically, lasted several seasons. When it started to fail, for what ever reason, the engine would over heat, the lights and buzzers would go off and the owner would know it was time for a new impeller.
The new model water pump had all the signs of a successful replacement to it's dependable predecessor, until that frightful day, when the new product was handed to "The Retail Public".

Note the ragged edge on the impeller sealing lip of the impeller on the left (red arrow). This impeller burned due to the ingestion of sea weed, and would operate at normal temperature up to 3200 RPM but the engine would overheat above 3500 RPM.  No real damage done because the  experienced owner  knew what to do and had the boat serviced.  The one on the right (blue arrow) cost the manufacturer an engine because the novice owner didn't notice the very slight increase in operating temperature. This owner continued to operate this engine for half a season until the engine just would not start. To make matters worse, the engine was replaced, and the new engine failed again, 20 hours latter. (shame on that dealership)
  The problem is air ingestion into the cooling system by the sterndrive water-pump. Instead of reduced water flow, like the old pump, when this pump fails, it sucks air.... and lots of it. So much that the temperature senders for the gauge and buzzer are fooled into thinking every thing is OK. When in reality the heads of the motor are hotter than Blazes.
Being careful and replacing this water-pump every season should keep you out of trouble, but watch that sea weed....

Note : There was a service bulletin concerning corrosion and this water-pump, as well. It should be referred to when servicing this water pump.  This corrosion Definitely will cause engine failure, if not attended to.... See additional info