Feb 12, 2017 · I made an off grid hot water system with an Espar D5 coolant heater/Isotemp Marine hot water heater, but haven’t yet plumbed it into the engine as an engine pre-heater. (and dual use like radiant heating or hot water). It is integrated into the Mercedes electronics pretty heavily. Doesn’t turn on if temp is above 38F or so. I don’t ...