I recently purchased a ‘06 Johnson 15hp outboard for my skiff project. It’s in very good shape, but the external anodes on the lower have a good bit of surface oxidation. Should I break into the guts of the case to inspect and replace the anodes in there too?
External anodes immediately take on corrosion and will look worn even if they are new. I recently cleaned my external anodes on a 2021 Tohatsu with CLR and a wire wheel - they looked exactly the same before I cleaned them after just one time in the water.
But….. at that engine age it is a good idea if the anodes are easily replaceable and you can get the parts. Definitely check the thermostat and replace if needed.
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Does it even have internal anodes? I don’t remember them on my older 2 stroke OMC motors…
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Well… apparently not. Somehow I got it into my head that these were anodes too (#’s 20 & 27), but marineengine.com says they are bushings instead. DOH!
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If anodes are corroding they are doing their job. No reason to clean them (coconut, you made me laugh out loud for real) or replace them unless they are really eaten up.
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Glad we got that figured out. lol
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LOL @Smackdaddy53 - glad you posted this - that’s always been my understanding, but I was suddenly wondering if I was missing something! Anodes are the only thing on a boat where corrosion is beatiful!
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Hahaha, yeah, I only did it because I was cleaning something else and had the solution ready to go. I pulled them to regrease and it was a slow day, so figured why not.
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Thanks for the feedback. I did a lot of NACE testing earlier in my career, so I am well aware of their function. The anodes on my Johnson… 
Are fairly well pitted under the oxidation on the surface so it is definitely time to change them.
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It doesn’t hurt to clean them but just don’t paint them…
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Confirming there are only external anodes on that engine. I know it well.
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So for the uneducated when should the external anodes be replaced? 25% gone, 50%?
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They say when they’re about 50% gone but I wouldn’t wait that long.
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