Ernest Christley <echristley@nc.rr.com> wrote:
>
> That's a lot bigger than the 5/8" tube I was thinking about when I
> started going down this mental journey.

   Umm, okay.  My primary frame of reference is automotive,
American made, ~5 liters, with large hoses to move a *lot*
of water.  At 5/8", your radiator is the equivalent of a heater core for the above mentioned car.  So ...
 
> pi are square...14 times 12 is 168...  gives 296.73 cubic inches..
> quick conversion with help of the internet says that is a little over
> one and a quarter gallons.

   Since the inlet is a bottleneck, let's try 3/4" hose.
197 cubic inches => ~7/8 of a gallon => 7lbs of coolant.

> ...
>
> But do I want to add 10lbs?  Does a long tube work well for a reservoir?
>

   Three pounds isn't *exactly* trivial, and 3/4" tube is
lighter than 1.5", but it also offers less surface area for
heat transfer - but honestly, the contribution is going to
be minimal anyway, just more than rubber hose would yield,
at less weight than rubber.  

   That latter, plus the rigidity of metal being more
resistant to collapse due to suction, is the main reason
you'll find early 90's GM intermediates (e.g. Buick Skylark)
using metal tubes and short hoses to connect them.

   The question maybe shouldn't be whether a pipe full of
coolant is a good reservoir, but whether you *need* the
extra heat-sink capacity (probably not).  But if you want
your radiator "back there", you have to get the coolant aft
and back, and with minimal frictional losses.  I don't have
data handy, but my suspicion is that, for the volume
required, 5/8" is pushing a little close to the edge for the
latter consideration.

Dale R.