Mercury Mariner 30/40 4-Stroke Outboard Service Manual 1998, Page 18Get this manual
MAINTENANCE
Corrosion Control Anode
Your outboard has control anodes at different locationsAn anode helps protect the outboard against galvanic corrosion by sacrificing its metal to be slowly eroded instead of the outboard metalsEach anode req uires periodic inspection especially in salt wate which will accelerate the erosionTo maintain this corrosion protectionalways replace the anode before it is com pletely erodedNeve paint or apply protective coating on the anode as this will reduce effectiveness of the anode1An anode is installed on the bottom of the transom bracket assemblyTrim tab is also an anode on the 3-14 in(83 mm) diameter gear caseThe 4-1 4 in(108 mm) diameter gear case has three anodesOne of the anodes is the trim tab and two anodes are located on the sideo