How to Clean a Mercruiser Lower Unit


One of the challenges for the Mercruiser owner and the do-it-yourselfer is cleaning the lower unit. This task is especially challenging if the boat has been in the water all season. Even in fresh water, opportunistic marine plants will grow in every nook and cranny of your stern drive. Follow a few simple steps you will have your Mercruiser lower unit looking like new again.

Things You'll Need

  • Scotch-Brite scrubbing pad
  • Scrub brush
  • Garden hose
  • Commercial hull cleaner
  • Rubber gloves
  • Eye protection
  • As soon as you pull the boat from the water, take it to a car wash and power wash the lower unit. You will have the best results if the marine growth does not have the opportunity to dry. Exercise caution and do not apply pressure directly to areas where water could be forced past seals and gaskets. Power washing will remove the heavy growth but will not completely clean the drive.

  • Follow the directions and apply one of several commercially available bottom and hull cleaners. Today's modern products make harsh chemicals like sulfuric acid unnecessary. Most instructions will have you either spray the product on or apply it with a natural bristle brush.

  • Allow the product to work for the allotted time and then spray with the water hose. A second application may be needed for the more resistant growth.

  • Remove the last of the growth with a soft Scotch-Brite scrubbing pad. Use caution and do not scratch the paint surface of the drive. Always wear rubber gloves to avoid contact with the hull cleaner. Always wear eye protection when using hull cleaning products.

  • Touch up any chipped paint with Mercruiser primer and drive paint. As an option, apply a foul-release bottom coating to the lower unit to make it easier clean next season.

Tips & Warnings

  • Only use commercial hull cleaning products in areas with good ventilation. Avoid breathing the fumes. Do not allow product to come in contact with your skin. Always wear eye protection.

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