Heat exchanger zinc

[John Langford]

I noticed a complaint in another thread about how hard it is to change the heat exchanger zinc. It reminded me that a very knowledgable (navy electronics guy) boating colleague  recently told me about his very novel (to me anyway) approach to heat exchanger zincs. His view is that most of the erosion of the heat exchanger zinc is due to the rush of water over the zinc and not from any electrolysis problems. He never uses normal zincs in his heat exchanger. Instead he threads a suitable length of soft steel bolt into the bronze zinc holder and substitutes it for the normal zinc. he argues that the soft steel is suitably less "noble" to handle any electrolysis issues and will not be subject to water erosion. It sounds convincing and I would love to stop buying zincs every 6 months. Any thoughts?

[Stu Jackson]

Four bucks or so is a small price to pay for regular zinc replacement.  I don't find it hard at all.  I made a note with a sharpie on the top of the HX that says: "11/16" -- which makes it easy to grab the right wrench every time.  I do it every three months with a written reminder on my engine maintenance log, and sometimes can replace the old one because it hasn't deteriorated much.  I use the boat at least once a week, so the engine hours are up there.  I find the access easy over the top and can reach in with one arm pretty easily (although this is an M25 which has more room, however, I did install a larger three inch HX a few years ago).  I was also doing some wiring below the aft cabin berth last week and could easily reach the zinc from there.  Call me a traditionalist, but with the relatively low cost and high benefit ratio, why mess around? (I can't comment on the electrolytic part of your post, John.)

[Ron Hill]

John : I agree with Stu that for $4 it's not worth saving or substituting anything for a Zn when you look at the price of a new heat exchanger!!
I understand that the M35B engine has much less access that the earlier M35A/25/25XP.  Not to sure if you can use the 1/2" Zn or you have to use the 3/8".  Another thing to check is the length of the Zn.  The inside of my HX is such that I have to cut off about 3/4" of length from a 1/2" dia. Zn.  In the Chesapeake I can get a 8 month season (200+ engine hrs) out of a single Zn as the water isn't as salty as the ocean. 
You might check if you can use the full length in your HX.  If you can then you can get a longer time between changes. 
A few thoughts.   

[John Langford]

Gentlemen,
It's not the money for the zincs which concerns me. If it is true that traditional zincs are overkill in this situation then the soft metal substitute would reduce the inconvenience of doing the change and (a big AND) would eliminate the problem of cleaning out the pile of zinc rubble in the bottom of the exchanger which the water erosion creates. If my colleague is correct, this is a much smarter way to go. I eagerly await further word from one of our electrical wizards.

[Ron Hill]

John : We all agree that ANY less noble metal will work (in theory). 
Why don't you try it with "a soft steel bolt" and then report back to us Board viewers - if it worked or didn't work!!