Richard, The pencil zincs in heat exchangers are notoriously undersized for what they have to do. The entire interior shell of the heat exchanger is bather in salt water, salt being a very active electrolyte. The metals of the "pac," cupronickel alloys, need to be protected against galvanic corrosion from the metals of the shell of the exchanger. The effectiveness of the zinc is based on the surface area ratio of the sacrificial anode itself to the surface area of the metals being protected. It's fairly obvious that the pencil zinc is at a significant disadvantage from the git go compared to the metals of the exchanger. Anode manufacturers want you to replace zincs when they are down to 50% by volume. Good idea in an expensive heat exchanger to do that. Do it every 60 days if you have to. If you don't, you'll get pinholes in the shell, and eventually, salt water into the fresh water side of the cooling system. It's unlikely that external electrical conditions would influence the rate of pencil zinc deterioration. AC doesn't cause zinc deterioration, but DC stray currents do. Those stray currents would have to be of the right polarization and flow end-to-end through the heat exchanger to eat up the pencil. Unlikely. What you can do is call the manufacturer's factory customer service number, and get to a factory tech support group. A local distributor is probably not going to know in the first place, and is probably not motivated to get you a good answer. You are all over a design issue with the engine, but I doubt your experience is greatly different from other engines. One other thing you might try is, contact the people at www.mrcool.us <http://www.mrcool.us/>. They make aftermarket replacement coolers for all kinds of engines, and their designs are more robust than OEM, at least in the case of my Cummins exchangers. Jim Peg and Jim Healy, living aboard Sanctuary http://gilwellbear.wordpress.com <http://gilwellbear.wordpress.com/> Monk 36 Hull #132 MMSI #367042570 AGLCA #3767 MTOA #3436