1987 Johnson/Evinrude CU Outboards 35A thru 55 Service Manual, Page 57Get this manual
AnodesTesting and Replacement Erosion or disintegration in salt or brackish water indicates the anodes are performing their functionThe anodes should be inspected and or replaced at intervals or corrosion of the engine will increaseI Note Ilf any anode has been reduced to two-thirds its original size (one-third eroded away) it should be replaced! To increase the duration of the anodic protection, the starboard stern bracket (on some models) is drilled to accept an additional anode
E.J to low ohms scale Connect one lead of the ohmmeter to powerhead ground and the other lead to the anodeBe sure surface of the anode is clean to make good contactOhmmeter should indicate very low reading (zero)If not, remove the anode and clean the area where the anode is installedThe mounting screws and the anode itself should also be cleanedInstall and retestI Note