Heat Exchanger Puzzle for Today

[Christian Williams]

Here is what I found several years ago inside the Hx: two busted-off zincs, trapped inside. Not unusual, since they corrode and break off if not changed on schedule.

But look more closely.

One trapped zinc is whole, including its threaded end. Riddle me this: how the devil could a whole zinc wind up inside the heat exchanger?

...

 

[Prairie Schooner]

Was that your first time opening the HX after purchasing the boat?

 

[Christian Williams]

Yep. I wonder if the PO intentionally "installed" a zinc behind the end cap.

 

[bigd14]

Maybe someone figured they would get twice the life if they just stuffed another zinc in there?

 

[peaman]

Riddle me this: how the devil could a whole zinc wind up inside the heat exchanger?

My guess is that some corrosion fouling had formed around the zinc just above the threads, and when the brass nut was removed, the zinc unscrewed and stayed behind. Assuming the zinc had corroded completely away, the mechanic simply inserted a new zinc, pushing past the previous one.

 

[Joliba]

My guess is that some corrosion fouling had formed around the zinc just above the threads, and when the brass nut was removed, the zinc unscrewed and stayed behind. Assuming the zinc had corroded completely away, the mechanic simply inserted a new zinc, pushing past the previous one.

This is very likely. Two years ago, after only one year with a magnesium anode (fresh water sailing only), I tried to exchange the anode. The anode had expanded as it degraded such that I couldn’t pull the spent anode out through its port. I left it for an additional season, then removed the exchanger for cleaning. By then the majority of the pencil anode had fallen into a chamber leaving only its supporting core behind.
I could have pushed the old anode in— threads and all —when I first found it stuck. My guess is that is what the PO of Christian’s boat did.