Corrosion Noted On Stern Drive

[Pendlm]

I have a Mercruiser 1982 MCM 228. I just had the boat in the water (Seneca Lake - a Finger Lake in NYS) for several days. Upon taking the boat out of the water (The boat is normally on a trailer except during periods of use), I noted some pitting corrosion on the stern drive. Four pictures are attached. The first two show the corrosion I observed. The second two show the sacrificial anodes (they don't seem to be sacrificing much!). Is it possible they need to be cleaned/sanded to better allow the metal surface to contact the water and do their job? Any thoughts are appreciated! I don't know much about corrosion control, but know that this whitish pitting is not normal. My boat has an aluminum prop if that matters.

Thanks,

Mike

 

[APPALOOSA2]

Re: Corrosion Noted On Stern Drive

First clean up that drive and get some primer and then paint on those spots.
Use some 80 grit sand paper on those anodes. That Stainless prop creates a lot of havoc with electrolysis.

 

[achris]

Re: Corrosion Noted On Stern Drive

Get ahold of a multimeter and check you have proper continuity between the anodes and the leg... You should have 0 ohms Between the anode and any and all parts of the leg....

Chris........

 

[Don S]

Re: Corrosion Noted On Stern Drive

That much corrosion after a few days isn't normal by any streatch. There could be problems with your anodes, or even the continuity system to the engine. May also be an electical leak in your boat, or even in the harbor where you were tied up. Here is a link to the corrosion prevention section from manual #6. Should give you some things to check.

http://www.boatfix.com/merc/Servmanl/6/6A7R3.PDF

 

[Pendlm]

Re: Corrosion Noted On Stern Drive

Thanks, guys, for the help. I checked for continuity between my trim tab and the stern drive. I had essentially infinite resistance - not good. I cleaned a small spot of the trim tab with sand paper and retested continuity between that spot and the stern drive attaching nuts. I had zero ohms. I removed the trim tab and sanded the whole thing. Now I have good continuity between the entire surface of the trim tab and the stern drive.

I still need to do my sanding and painting.

Also, a question: What is the function of the the two acorn anodes. I have continuity from what they are mounted on to my stern drive attaching nuts. However, I do not seem to have continuity from the acorn anodes themselves to anything?? Even after sanding them clean. Is this a problem? How are they fastened on?

I'm still going to do some more poking around, but feel I'm on the right track with your help.

Thanks,

Mike

 

[APPALOOSA2]

Re: Corrosion Noted On Stern Drive

They just screw on, you can take a pair of channel locks and unscrew them to sand if you would like.