CORROSION PREVENTION AND MAINTENANCE
Page 6 of 16 APRIL 2002 2002-06
This document is provided to be used for solely and exclusively by the original recipient and as prescribed by Mercury Marine and may not be
distributed or copied, digitally or otherwise, without the prior written consent of Mercury Marine.
Step by Step Procedures when checking a boat for a
Corrosion Problem at the Location where the boat is normally moored
Tools Required:
1) Digital Multi-meter (VOA)(volt/ohm/amp) (91-854009A 3)
2) Quicksilver Reference Electrode tester (91-76675T1)
The first five things to check before performing any test:
1) If equipped with shore power, unplug the shore power.
2) Check the fuse in the positive (+) battery lead.
3) Check the battery voltage, the voltage must be 12.6 volts or higher.
4) Check for loose connections at the controller and at the battery. All connections must be
tight.
5) Check the ground between the drive and the controller.
Step 1) Before performing corrosion testing.
The boat should be moored (without being operated) for at least eight hours before perform-
ing the test. This is necessary to allow the MerCathode System and/or the sacrificial anodes
to polarize the water molecules in direct contact with the drive. Be careful not to rock the boat
excessively while performing the test, as this will alter the test readings.
Step 2) Checking for conductivity, using the following method.
1) The boat must be moored in the water when performing this test.
2) Using a digital volt/ohm/amp multi-meter set on DC volt scale set the meter on 0-2 volt
(0-2000 millivolt) scale.
3) Connect the negative (black) (–) meter lead to the multi-meter, then connect the lead to
the negative (–) battery terminal.
4) Connect the (red) positive (+) meter lead to the multi-meter, then suspend the lead in the
water within (152mm) 6” in. of the aft end of the drive unit. (Do not allow it to make con-
tact with the drive unit or the propeller) for this test. The reading should be above 3milli-
volts.
5) Next connect the end of the positive meter lead to each metallic component on the stern
drive and transom, making sure that there is good electrical contact to each surface. The
reading should drop below 2millivolts.
6) A reading higher than 2millivolts indicates an improper grounding circuit.
