The corrosion warranty is for three years from the original date of purchase of the complete power package for 1988 and newer MerCruiser product that have a one-year limited product warranty. See the complete corrosion warranty under the section titled Warranties or in your owner's manual. Protection against certain types of corrosion damage must be provided by using such systems as the Mercury Precision MerCathode system and/or galvanic isolator. These certain types of corrosion damage include damage due to stray electrical currents (on-shore power connections, nearby boats, submerged metal), etc. It is the owner's responsibility to ensure that all necessary anti-corrosion devices are in good working order and are providing adequate protection.
The Mercury Precision MerCathode system provides automatic protection against galvanic corrosion. It is a solid-state device that operates off a boat's 12-volt battery and provides protection by impressing a reverse blocking current that stops the destructive flow of galvanic currents. If your power package does not come already equipped with a MerCathode system, Mercury strongly recommends that you install one, particularly if your boat is equipped with a stainless steel propeller or other submerged stainless steel hardware.
The Mercury Precision Galvanic Isolator is a solid-state device that is series connected in line into the boat's green safety grounding lead ahead of all grounding connections on the boat. This device functions as a filter, blocking the flow of destructive low voltage galvanic (DC) currents, but still maintaining the integrity of the safety grounding circuit. A galvanic isolator is only necessary on boats utilizing a shore power connection.
One of the first signs of galvanic corrosion is paint blistering (starting on sharp edges) below the waterline, with a white powdery substance forming on the exposed metal areas. As the corrosion continues, the exposed metal areas will become deeply pitted, with the metal actually being eaten away. Galvanic corrosion of aluminum sterndrive units, or any other underwater aluminum on your boat, is accelerated by attaching stainless steel components like propellers, trim planes (if connected to engine ground) and after-market steering systems. Whenever you add stainless steel accessories, itís a good idea to have the corrosion resistance checked to make sure it is still adequate.
Stainless steel propellers can discolor and form areas of light rust. Brushed finish stainless props are more susceptible than brightly finished stainless steel props. Rust stains can occur from polluted water, galvanic corrosion from the boat or marina, or from oxygen depletion. The propeller can be easily cleaned with rubbing compound or Scotchbrite. Do not use steel wool. After cleaning, use chrome polish to protect the finish. Stainless steel props can also turn white from calcium or lime in the water. In this case, clean the prop with household mineral bath and tile cleaner. Again, do not use steel wool. Follow-up with chrome polish to protect the finish.