Re: corrosion gear case
There are many combinations of reasons why the lower unit has corrosion, but most have at least some corrosion problems. <br /><br />When the unit is in the water, it is like a large anode. To protect it from direct exposure to galvanic corrosion, it needs a combination of non-metallic coatings and sacrificial anodes. <br /><br />The forward end of the lower unit is subject to more abrasion than any other part and is the first to have the coatings stripped away. If water gets behind the surface paints it continues to accelerate the corrosion even when the motor has been carefully washed down and is otherwise dry.<br /><br />The anodes need to be replaced when they are coated, not when disintegrated.<br /><br />Annually, the lower unit should be completely cleaned and coated with one of the many lower unit paints designed for that specific purpose, many of which are branded or recommended by the outboard manufacturer. Additionally, a clear coat of lower unit paint should be applied.<br /><br />Most boat bottom paints contain some metallic component and, therefore, can only worsen the problem.<br /><br />Generally, the more chemical content the water has, the better a conductor it is. Acid ponds, muddy rivers, and alkaline tributaries are worse than clean water bodies with neutral PH. Salt water is a great conductor.
