Frequently Asked Questions

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MerCruiser Corrosion


When my boat is stored in the water, should my sterndrive be stored in the “up” or “down” position?


Sterndrive should be stored in the down position to ensure that the anodes are in the water for maximum corrosion protection.


My sterndrive paint is peeling and/or blistering. What is going on?


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, it's a good idea to have the corrosion resistance checked to make sure it is still adequate.


What is the length of the corrosion warranty?


The corrosion warranty is for three years from the original date of purchase of the complete power package for 1988 and newer MerCruiser product. SeaCore models receive a four-year limited corrosion warranty. See the complete corrosion warranty under the section titled Warranties or in your Operation, Maintenance & Warranty 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.


What is a galvanic isolator and what does it do?


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.


What do I need to know about corrosion?


The good news is that corrosion can be prevented! Marine corrosion is a fact of boating life, but you can protect your investment with diligence & proper maintenance. As the boat owner, YOU are the most important key to effective corrosion protection. Here are some things you should know:

All MerCruiser sterndrives come standard with aluminum sacrificial anodes a three-year warranty against certain types of corrosion (see your Operation, Maintenance and Warranty manual for more details). SeaCore models receive a four-year limited corrosion warranty.

Bravo sterndrives are also equipped with a MerCathode, optional on Alphas.

Magnesium anodes are suggested for fresh water use ONLY & can be purchased from your authorized dealer.

Anodes & sterndrives should be inspected on a regular basis for signs of corrosion. Do not paint anodes.

Not all anodes are created equal. Don't sacrifice your sterndrive's protection with the use of poor-quality aftermarket anodes.

The MerCathode should be tested annually by an authorized dealer for proper operation. Do not paint or power-wash the MerCathode.

Your particular boating environment may require that you install additional anodes or other protective devices.

Whenever you add stainless steel accessories (for example props or trim tabs) it's a good idea to have the corrosion resistance checked to make sure it is still adequate

If you use shore power, you should have an approved galvanic isolator installed to protect against stray current corrosion (electrolysis) from your dock, from your boat's accessories or from other nearby boats.

Corrosion can be caused by many factors, such as the wrong type or improper application of anti-fouling paint, marine growth, stray electrical current (electrolysis), an improperly wired or damaged MerCathode, etc. These types of conditions are not covered by the warranty.

Before you notice signs of corrosion, contact your authorized MerCruiser dealer to arrange for an in-the-water hull potential test where the boat is primarily moored. This test will help the dealer determine if your protection level is adequate.

See your Operation, Maintenance & Warranty manual for more information.

A very informative pamphlet on corrosion "Marine Corrosion Protection Guide" (#90-88181301) is available. Please call 1-800-MERCURY to request one.


What is a MerCathode and what does it do?


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 MerCathode should be tested annually by an authorized dealer for proper operation.

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