Boat owners with an inboard engine will know the symptoms – the engine, which normally runs perfectly at the right temperature, has recently started to run a bit hotter. This may only be evident when you push the throttles hard – the temperature gauge slowly starts to climb. Or perhaps even at cruise speed, near the end of a long run, when you find the needle is sitting a bit higher than it used to.
The reason, obviously, is that the cooling system is not as efficient as it was before. And the most likely cause is that the fine tubes of the heat exchanger are starting to get covered in calcified deposits. Of course, there could also be physical impediments like a blocked water inlet or broken rubber fingers on the water pump impeller, but those
