Most instant water heaters require a drop in output line pressure to turn them on. Probably not going to be able to use a heat exchanger to preheat the engine unless you are cycling water through the unit continuously.
Also, if you put it in the engine compartment, how are you going to keep the lines to and from it from freezing when not in use. Also, the heater itself might be at risk of freezing when not being used. craig
Hey Ron. I just purchased your old 4905. Anything I need to know. Where did it come from? larrydbaker@netscape.net
I did just what you are talking about, I can heat my coach, pre heat the eng. and my domestic hot water. I have a precision temp lp unite. Or I can do all the same from the eng while traveling.