Originally Posted By: SHOZ
If the coolant has dissolved minerals in it then it grounds that way. That is what the millivolt check is good for, determining the amount of mineral content in relation to millivolts.
A good reason to use distilled water when you fill.
But I guess I need to go see if any of my cars radiators are grounded. Only one has the all aluminum radiator. The other has the plastic tank style that would not be grounded.
Just additional info/thinking: The electrolysis/corrosion actually needs both-- the full circuit, to occur. It is exactly that-- a full circuit. Break apart the circuit and the reaction stops. In this case, vehicle ground would be one "wire" and the minerals through the coolant the other. due to different attraction properties between the radiator and engine, ions would pull material from one, and plate them to the other, traveling through the coolant (electrolyte, as it becomes in this case), with the vehicle ground being the return path for electrons. This is the exact same principle in how a battery works.