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Galvanic corrosion of boat engine

Hi all,

I have just built a heat exchanger for a fresh water cooled pleasure craft. This serves as a cooler for a car type V6 engine which has cast aluminium components and a cast steel block. The heat exchanger is made from copper. The exchanger does not touch the engine physically, and the only commonality they share is the fresh water passing through both. I am not sure whether this scenario has all the right qualities to cause galvanic corrosion or electrolytic corrosion. I was considering placing an anode inside the cooling system in contact with the aluminium components just incase.

Eternally grateful for your thoughts.

John Gray
hobbyist - Perth, Western Australia, Australia
2004

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The 'right qualities' needed for galvanic corrosion include a metallic current path as well as the liquid current path, so the copper exchanger cannot cause galvanic corrosion. The cast aluminum components will be anodic to the cast steel block though. Consequently, an anode could be beneficial. I understand that anodes must be magnesium rather than zinc to be useful with fresh water.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004

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Anytime we have dissimilar metals and water we have set the stage for galvanic action to occur. Most all marine shops should be able to get zinc 'sticks' for you, these sticks can be found in various shapes and sizes, commonly used in the cooling system as a 'sacrificial metal' to help control electrolysis.

Replace a fitting or two in you plumbing with a similar fitting that also has a smaller hole for a 3/4 inch pipe plug, use the zinc stick that comes with a 3/4 pipe plug on one end. Buy spares, you can screw them on/off the special pipe plug.

Depending on the hours of service you will figure out the service life of the size sticks that you are using. Visual inspection alone is not enough, zinc can 'honeycomb', always tap the zinc to ensure it is still solid. Replace the stick if more than 50% used.

Do this on BOTH the fresh-water system and on the raw-water system. Preferably 2 places in each system.

I have further slowed the galvanic process on raw salt water plumbing by linking the pipes across the hoses with stainless cable and hose clamps, making a direct metal to metal path bridging the pipe gap formed by any hose.

Charles R Berg
- Wright City, Missouri, USA
2004





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