03-11-2012 03:57 - edited 03-11-2012 04:00
There are 3 zincs (anodes) on your motor. Normally you only have to replace the one on the back of the gearcase just above the anti-ventilation plate every 1 to 3 years if used often in saltwater areas. One other is a large heavy bar shaped item underneath the trim and tilt unit and that one lasts for a very long time if everything is in good shape. The third is inside the gearcase exhaust area on the underside of the propshaft bearing housing. It normally doesn't require servicing and you have to remove the housing and bearing assembly for access.
If you are eroding the anodes very quickly may you have have a problem with stray currents from either the boat's electrical system or from nearby electrical problems caused by neighboring boats or shore current from the dock's 120 volt system. Having copper based bottom paint will accelerate anode wear also. Another culprit is the use of automotive portable battery chargers while a boat is in the water.
If severe, you may have to enlist the services of a marine electrician to check the environment for leaking electricity. Look for someone ABYC certified.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.