Posted for Mark Steitle <msteitle@mail.utexas.edu>:

David,
Won't a system as you have described stop pumping much sooner in the
event of a leak, or low coolant level?  It seems to me that low coolant level
would allow air to be sucked into the return lines to the wp and cause the
wp to loose its prime, thereby shutting down your cooling system.  That
could ruin your whole day.

Mark S.