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Originally Posted by redleader
Won't help. He confused about how the battery effect works. The reaction isn't directly between the two materials, but rather between one piece of metal and dissolved ions in the coolant. Having a common potiential between the two metals doesn't affect the dissolved ions.
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This is the same exact thing as what I previously discussed except now the corrosion cell is taking place on a single object. Here the circuit takes place when one area of the same metal becomes more anodic compared to another area. This causes a potential imbalance on the metal surface. The anodic area (say a spot on a waterblock where the paint is missing), provides current to the cathodic area around it. Over time this can result in metal loss at the anodic area. Eventually you can get pitting and all of that action. This often happes with poorly galvanized or poorly anodized materials. As it starts to wear off the exposed areas form a corrosion cell with those areas that are still covered. Here, the electrolyte could be condensation, water inside the reservoir, steam, or who knows what. So to eliminate the problem you have to cut part of the circuit. Since this occurs within a metal you are somewhat limited to your options. Typically the problem is solved by removing the electrolyte or insulating the anode from the corrosion (by recoating).