TROUBLESHOOTING
SERVICE MANUAL NUMBER 28
90-863160 MAY 2000 Page 1C-33
Testing Procedure for Corrosion Protection
1. Unplug shore power (if equipped).
2. Measure hull potential with silver/silver chloride reference electrode and digital volt/ohm
meter.
READINGS
Potential Diagnosis
Below 850 millivolts
Drive is corroding.
(Refer to “Drive Corroding”)
Saltwater
Between 850 - 1100
millivolts
Drive is protected
Above 1100 millivolts
Drive is overprotected.
(Refer to “Drive Corroding”)
Potential Diagnosis
Below 750 millivolts
Drive is corroding.
(Refer to “Drive Corroding”)
Freshwater
Between 750 - 1050
millivolts
Drive is protected
Above 1050 millivolts
Drive is overprotected.
(Refer to “Drive Corroding”)
CORROSION SYMPTOMS
• Paint blistering (usually on sharp edges)
• Loosely adhering white corrosion products on exposed aluminum surfaces (do not
confuse these with tenaciously clinging calcium carbonate deposits)
• Aluminum pitting
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