Quote Originally Posted by dr. d View Post
"Grounded" can be a good thing or a bad thing, depending on what we are talking about.
i am confident that the gasoline engine won't run if there are no electrical currents running thru it, as measured by the multimeter..
perhaps what you mean is, the engine should be well-grounded, to avoid electrolysis from stray currents..
heck, when your engine is poorly grounded, the radiator is going to be the least of your concerns.. a poorly-grounded engine won't run well, won't charge the battery well.. it might even interfere with the electronic entertainment systems..
Technically if one needs to be more precise, the engine has to be earthed properly.

And since we're being specific here, though it is the nature of the coolant, being electrically conductive, and the differences in the activity of metals in the cooling system that will not tolerate a higher amount of stray voltages. It does require quite a bit of voltage (relative to the mass of the materials in the system) to get the galvanic process started.

Readings on your multimeter on voltage setting should read at practically 0.0 when the engine is shut off. Though it isn't unusual to have a 0.1V reading, anything above that level is cause for alarm.

At the risk of being more esoteric, there are instances wherein the coolant chemistry changes well enough that in itself causes the galvanic reaction to begin. This normally occurs when incompatible additives are added to the mixture causing a shift in the ph of the coolant. This is when one would need to flush their system and rinse it as well as one possibly could.

Note that this tends to happen more with aluminum radiators. So be wary in tampering with the stock mixture.