Which of the following is NOT one of the recommended engine maintenance tips?

Changing the spark plugs regularly is indeed a vital part of engine maintenance and is recommended to ensure the proper functioning of the engine. Spark plugs are crucial for igniting the fuel-air mixture in the combustion chamber, and neglecting to replace them can lead to engine performance issues, misfires, and reduced fuel efficiency.

On the other hand, keeping the engine well-tuned and lubricated, checking oil levels and changing the oil, and checking batteries for any loose connections are all essential maintenance tasks that contribute to the longevity and reliability of the engine. These activities help maintain optimal engine performance and prevent potential mechanical failures. Regularly changing spark plugs is aligned with best practices in engine maintenance, making it an essential part of the overall upkeep of a boat's engine.