Fresh water flush and pencil zincs

[John Larson]

Quick question… As an adherent to Tony’s fresh water flush regime on our 6BTA… What effect, good or bad, does this have on the three pencil zincs in the engine cooling system. It appears the bottom zinc in the aftercooler is the only one that sits in water when the engine is off.

Thanks much…

John

Topic

[Woo]

I operate in salt water, and proactively fresh flush, engines off.
Pencils last longer for sure, however, are still doing their job for the hours the engines are run.
Pic of one of my aftercooler’s end caps attached. Pick which one lays in fresh water
The bottom aftercooler cap (the brown tinged), immersed zinc was fairing a little better, however, not so good that it would go say, another year. I easily got 3 years from my pencils but your experience may differ.

[Brad Arrington]

Would like to know how your zincs faired when you check them.

I’m afraid I’m just slightly too lazy to close my sea cock when flushing. It’s mounted outboard and forward of the exhaust side, and requires either laying across the engine and a long reach, or some yoga moves to get to it. I also like backflushing and ensuring I don’t over pressure the system with dockside water pressure.

My generator zinc probably faired better. That will have a comparatively larger flow of fresh water due to the smaller raw water hose diameter.

[John Larson]

All fresh water

Thanks Brad. I do an all fresh water flush with seacock closed. I’m almost due for external zincs so when I do that I’ll inspect the engine pencils to see how they’ve faired in a fresh water environment.

John

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Brad Arrington

[Brad Arrington]

Still needs maintenance

Comments based on the QSC 8.3 600 in my boat. This was my first season with the boat, and prior to launch I installed strainer flush caps. I consistently flushed the engine after every outing for minimum 5 minutes. Process was to connect the hose to the flush cap and open the valve – the 2″ seacock was not closed.

My zincs were changed April 28. I checked them at layup, November 12. The aftercooler and heat exchanger zincs were not eroded, but were soft and starting to spall a bit. They will need to be replaced.

The fuel/oil cooler zincs were well eaten.

Perhaps if I closed the seacock there would be less mixing and the zincs would last longer.

[Author]

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