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IF the coolant is still conductive, they did not refil with distilled water as you are supposed to, or did not flush the system as they were supposed to, and you are running around with old coolant.

ANY SET OF DISSIMILAR METALS that are connected with a conductive material, IE actually bolted together, or wires attached, or in a conductive solution will experience some type of galvanic corrosion.
The best way to treat this problem is to isolate the two parts. Since this is not normally possible, the next choice is to put in a sacrificial anode.

Depending on the materials and the amount of conduction, the decay will vary. So some people never see an issue. My bet is those people change out their rad fluid pretty regularly. Or it is so deep into the engine they cannot see it.

Good ground help, but do not prevent. Since it isn't about having a better path to ground, rather the metal's desire to giveup or take an electron from the other metal. ...



Under 400mV or .4 volt seems to be generally accepted OK in auto repair.

Andrewh, do you see an issue if it's not absolutely dead nuts zero mV ?? I've seen many that still have some mV in them after complete flushes.

If somebody did a heater core and forgot to put in a ground strap or other repair, you'll have a continual problem.

Some particular car models more often than others have premature heater core corosion from grounding issue.