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

     Matt Prather wrote:
     >
     > I don't think you get enough temperature rise by just piping air off
     > the back side of the radiator - especially in the winter when you need
     > the heater the most and the input air is the coldest.  You could put
     > a winterization kit of sorts on it.  Feed cabin air via scat tube up to
     > a duct mounted on the corner of the radiator, and then heated air from
     > the same corner of the radiator back to the cabin.
     >
     > It still seems slicker to mount a small heater core in the cabin.  Maybe
     > slightly heavier, though.
     >
     > Regards,
     >
     > Matt-

Those are good points. The reasons that I decided to try taking hot air off the back of the radiator  are these-

Elimination of the weight of a heater core.

elimination of potential failures of two heater core hoses, and at least four fittings.

Also, I'm using a cowl flap, so I shoud be able to control the coolant temperature. with the cowl flap, I should be able to almost completely close off the exit air from the cooling system if I
wanted to.  If this scheme doesn't provide me with enough heat, I've got a heater core sitting on the shelf, it would be no real problem to install it later.

Brian Trubee

Rv-4, hoping to be done by next summer.

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