I would not expect 321 to crack and fail in thermal  cycles  below 1600
     > degrees.  I don't know how
     > hot the cool tube will become but if it does not reach 1600 degrees
     > then no problem, ever.    Jerry

Jerry, my two cents worth is this- why risk it? I thought I'd just use a heater core since we are using a liquid cooled engine, but then I saw that someone (don't remember who) just took air from
the back side of the radiator. This way, you don't  have the worries of an exhaust leak, and don't have the worries of the weight and potential failures  of a heater core.

Brian Trubee

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