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Years ago, following Tony’s recommendation, I hooked up fresh water flush fittings to my engine’s strainer and started flushing religiously. Within less than a year I noticed that the engine zincs were holding up much better; in fact after three years they are still going strong. I also believed that I was reducing corrosion on my raw water metal components, particularly the after cooler. Tony has implied that you can double the interval between after cooler servicing if you flush with fresh water.
But now I have doubts about both zinc wastage and the impact on the after cooler with fresh water flushing. Here is why:
A bit of research indicates that zincs in fresh water form a protective coating that doesn’t allow an further wastage. That is one reason why my zincs have lasted for more than three years. But a question remains- does that protective coating also mean that the zinc doesn’t do any good when you go cruising for a few days in sea water? My guess is that the zinc does not do any good.
Further research indicates that for both fresh water and sea water use you should use aluminum anodes. These are available from boatzincs.com for hull anodes but not engine pencil zincs. Performance Metals is the only manufacturer that I have found for aluminum pencil zincs which they call Navalloy. Unfortunately Performance Metals doesn’t sell to the public, a review of some of their distributers comes up with only one that has aluminum anodes and these are for outboard engines, and finally Performance Metals hasn’t responded to my email asking where I can buy their pencil zincs. I can only conclude that the average boater will have a hard time buying them.
But what about the benefits to the after cooler of fresh water flushing, which was the primary reason that I started doing it. After cooler corrosion is real and results in failed after coolers and possibly failed engines if it isn’t corrected. My own limited experience indicates that corrosion starts on the aluminum housing surfaces, probably due to condensate combined with salt air corroding the aluminum. Fresh water flushing will do nothing to stop this.
I have reviewed perhaps a dozen pics of corroded and failed after coolers and they all have extensive aluminum corrosion. Some also have minor corrosion on the bronze tube sheet which is exposed to sea water, but I suspect that it is caused by the o-ring seal failing and then galvanic action between the aluminum and bronze causes pitting on the bronze.
So, if zincs won’t work with fresh water flushing, you can’t buy aluminum anodes, and it won’t help prevent after cooler corrosion- then why do it?
David
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