Mercury 565 Manual page 89

Using magnesium anodes in salt water causes an electrochemical reaction
on the metal surface of the drive, resulting in corrosion damage from the
paint blistering and peeling off the drive. Use magnesium anodes in fresh
water only.
IMPORTANT: Mercury Marine recommends installing a MerCathode system or
anti‑corrosion kit whenever using a stainless steel propeller, or if the boat is
equipped with stainless steel components immersed below the waterline that
are connected into the engine ground system. If a boat is equipped with
stainless steel aft planes, a large anode should be installed on each to handle
the increased galvanic corrosion potential.
Replace the sacrificial anodes if eroded 50% or more.
Mercury Marine recommends using anodes sold through Mercury Precision
Parts only. Some other manufacturers of aluminum anodes use alloys that are
insufficiently pure to adequately protect critical drive components for the
duration of the anodes' expected life.
MERCATHODE SYSTEM
The MerCathode system should be tested to ensure adequate output.
NOTE: This test should be made where the boat is moored, using a reference
electrode and test meter. Contact your authorized Mercury MerCruiser dealer
to arrange for this test.
SACRIFICIAL ANODES
Sacrificial anodes help protect the power package against galvanic corrosion
by sacrificing its metal to be slowly eroded instead of the metal components on
the power package. These anodes are installed at different locations on your
power package.
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MAINTENANCE
NOTICE
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MerCathode
Electrode assembly