Zinc VS Magnesium

Newsgroups Archive Prior to 2025
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Has anyone used a magnesium anode for the engine anode in the heat exchanger?

Before there was just a zinc engine anode and a zinc on the prop shaft. Neither seemed to wear out very fast.
A few years ago I switched to a magnesium anode on the prop shaft because that’s what the marina sold me saying they only sell this type now. It is fresh water.
This shaft magnesium anode has deteriorated quickly and needs to be replaced.
However the last engine zinc seems to be like new. It is not a magnesium but rather a standard Westerbeke replacement zinc.

I’m wondering if the shaft anode took all the load and now the engine anode is not doing much.

I see you can buy magnesium engine anodes on line that will screw into the 1/4npt plug the old Westerbeke anodes used. The original zinc is 3/8 x 1 3/4 inches.
https://www.boatzincs.com/engine-magnesium-only-sizes.html

Is there any reason why I should not be using a magnesium anode in the heat exchanger?

Tom
26C #28 with a W13
Penetang

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https://www.boatingmag.com/how-to/choosing-right-sacrificial-anode/

What I take from this. At a dock plugged in use zinc. Otherwise magnesium. If you use zinc, buff it shiny or change every two years regardless of wear.

3

Hmm. The boat is rarely plugged in for long.
Looks like I have to get the magnesium pencil anodes. The Westerbeke one would be zinc. I can’t find a supplier here in Canada so boatzincs.com.

Tom