Ideas to stop corrosion in aluminum heat exchanger?

[s/v Jedi]

This comment isn’t about fixing this but more about preventing it in the future:

You have a ground/negative electrical connection on the engine, which connects the alternator and starter to battery negative, as well as probably some grounding/bonding wires etc.

Buy a on/off battery switch and move all those cables to one side of that switch and a properly sized jumper between the switch and the engine block connection point.

Keep this switch off when the engine isn’t in use.

[bil56]

in an aluminum alloy heat exchanger, Al/Mg rather than Zn anodes would be needed ...

[boatpoker]

Originally Posted by bil56

in an aluminum alloy heat exchanger, Al/Mg rather than Zn anodes would be needed ...

Our new engine with aluminum heat exchanger came with a zinc anode, it was completely wasted in 30 days. We are now in our 3rd month with an aluminum anode showing approx 15% wastage.

[Parallaxcat]

Originally Posted by fourlyons

I got no response last time I posted this so I'm going to try again.

I recently bought a older, used Nanni 3.75he, it is a 21hp Kubota block.

The heat exchanger was leaking antifreeze slowly from below the exit cap for the tube stack. I discovered an epoxy repair, that has failed, to an area of corrosion in the aluminum just inside the bore where the exit end of the tube stack is capped. The corrosion is inside the freshwater chamber, again in the aluminum, so it shouldn't be due to saltwater. The tube stack is a copper alloy, but it is, in theory, isolated from the aluminum by the o ring and paint. Plus, there is no corrosion at the other end of the tube stack where it sits in an aluminum bore.

I have ground out all of the corrosion, cleaned it, epoxied, and trued the bore. It no longer leaks.

My question is, why did it corrode, and how do I keep it from corroding in the future?

Is it possible it's as simple as the anti corrosion additives in the antifreeze went away because it wasn't changed often enough?

Should I add a zinc to the freshwater chamber, I didn't think antifreeze is an electrolyte, so one shouldn't be needed, right?

Thanks

Hi exact problem with Nanni 4.150he including previous epoxy repair
M’y theory is the exchanger seal itself was leaking in and around the bore now somewhat heated salt water. Now you have a path and electrolysis followed