Graeme Robinson writes: “At the end of the sailing season I always clean up my 5hp Yamaha outboard. One exercise is to run it through with fresh water, which I do in a large size garden trug.

“Is there any additional outboard cleaner solution which can be added to the fresh water which would dissolve any accumulated salt water corrosion internally?

PBO engine expert Stu Davies replies: “Let’s start by saying that having taken apart many direct salt water cooled small auxiliaries, I can safely say that the deposits can range from hardly anything to almost complete blockages of the cooling channels.

“Depending on which part of the engine, they can be mixtures of carbon, salt and aluminium salts. The deposit around the exhaust outlet can be particularly hard, and is not an easy mix to simply dissolve. There is an argument for flushing after every use if not used regularly.

“My regime on my 2.2hp Mercury 2-stroke is to take the split pin out of prop and then slide the prop off (the engine is a direct drive and this stops us having a spinning prop in the bucket). A bucket of fresh water can then be slid on to the bare leg and the engine started and flushed.

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“But are there any outboard cleaner products that actually dissolve deposits? A note of caution, our small outboards are made of aluminium, easily dissolved by strong acids which dissolve ‘salts’ so a DIY product mix is not recommended.

“That takes us to a proprietary product such as Rydlyme’s biodegradable marine descaler. They sell a kit to do exactly what you want to do.

“Also, don’t forget to drain the fuel tank and the carburettor. Just turning off the fuel tap and letting it run until it stops doesn’t hack it.

“The small amount of fuel left in the float chamber will still cause problems when it evaporates.”

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This feature appeared in the Summer 2023 edition of Practical Boat Owner. For more articles like this, including DIY, money-saving advice, great boat projects, expert tips and ways to improve your boat’s performance, take out a magazine subscription to Britain’s best-selling boating magazine.

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