Using exhaust heat as part of a WVO system always sounds like much better of an idea than I believe it would be in practice. The biggest problem I have with it is the inconsistency. The temperature extremes seem to me to be just too large to make it practical. Coolant heat, on the other hand, is regulated by the thermostat so at least you know what you are getting.

But, as I have said before, much of the WVO world of today is built on the wild-eyed experimentation of others in the past so if you feel you can make it feasible, try it out. Just don't have a steam explosion or burn the car down in the process...

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Keep everything as simple as possible-but no simpler--Albert Einstein