[77newell]

I believe the coolant level sensor is a 2 wire device that should be electrically isolated, ie; it should not be allowing electricity to escape into the radiator. Testing it would require removing it, energizing it and checking for voltage on the case.

If it is OK, then life gets more complicated. You then have to consider 2 possibilities; current flowing through steel framing parts and using the radiator as part of the path, or the engine is inadequately grounded and the coolant is carrying some charge that gets grounded through the radiator.

If the structure around the radiator isn't all welded together or otherwise electrically bonded, I would install grounding wires between the various parts and then to a secure grounding spot.

Regarding the engine grounding I would want to make sure there were good grounds on both the block and the head as these are where stray currents could access the coolant.

I'm not sure I'm being helpful here, but hopefullyam