I have a generic concern about water heaters that use engine coolant as
the heat source: a pinhole leak in the heat-exchanger tubing inside
the water heater would permit coolant to mix into the hot water, and
you might not know it until the leak became severe. Ethyl glycol is not
my favorite intoxicant!

Anyone aware of any instances of this (presumably, there would be a
lawsuit)? Are my fears unfounded?

Capt Ron