Glad I checked!

Last weekend I spent fueling the boat and getting the dinghy davits straightened out on the boat for the move to the Bahamas. I found that the carburetor on the dinghy motor was leaking so I had to replace some gaskets (just replaced them last year too!)

This weekend was spent cleaning and checking things in the engine room.

As part of that I checked the engine zincs. On one engine the zinc was broken off so I had to open up the end of the heat exchanger. When I did I found 5 pieces of the impeller. Oddly this engine has not run hot nor had it noticeably decreased in any water output. The impeller has about 350 hours on it so I would call that a win.

One thing I noticed was that in the other engine, the zincs were pretty much still intact. This has been the case on all but my generator zincs to include prop shaft zincs.

Why would this be? I’m in fresh water normally so going out/ back in always has us “flushing” the motors.

Are you in a marina? I have found that when other boats electrical cords are in the water, my zincs eat faster.

Not quite sure which you're questioning. The zinc broke off, the impeller disintegrating or the fact that it hadn't overheated? I would call it a win only in the respect that you caught it before it got worse and did overheat. At high speeds the impellers tend to act somewhat like centrifugal pumps, but even so, they'll eventually not pump enough. During normal service I found my generator impeller had lost almost ALL of its blades yet the generator ran and seemed to pump normally. Go figure. As to why the impeller might have started falling apart - it could have been old stock when you put it in.

Ken

More along the line of why some zincs would be wasted away while others in the second engine would not.

Perhaps the zinc in the other engine does not have a good electrical connection to the body of the exchanger.

Ken

What ken said. Test zinc to engine connection with an ohm meter.
You don't say if this is a new to you boat but it in not uncommon for people not as thorough as you to just shove a new zinc in while leaving the old pieces to plus up coolers.

I have owned the boat for five years. It is always been this way though.

k9medic said:

I have owned the boat for five years. It is always been this way though.

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There are only 2 reasons I can think of that a zinc will not "waste away" (which means it is doing its job). 1. It can't do its job (not electrically connected to the items it is supposed to be protecting) or 2. It has no job to do. The item(s) in question do not generate current flow - which is a simplified way of saying there aren't 2 dissimilar metals in electrical contact immersed in an electrolyte (conductive water).


Ken

If I understand you correctly the anodes have been there for 5 years and have not shown any wastage. If this is correct then they are indeed doing nothing. Maybe they are not installed properly, teflon tape on the threads or something similar? Are they indeed zinc? What are the other boats nearby using for anodes? Zinc, aluminum or magnesium? If you are in fresh water only you do not want zinc and that could be why they are not doing anything. If you are in both fresh and salt water, then you should go to aluminum. If in fresh water only then either aluminum or magnesium is good.