Posted for Jim Sower <canarder@starband.net>:
<... spare pump could be used and still be lighter than the
mechanical pump ...>
How about a 2-stage system.  A small pump, say where the coolant
enters the block from the radiators that just pumps maybe 30% -
40% of what is required, but would be adequate to get you on the
ground in case of a main pump failure.  This "background" pump
would work all the time (except perhaps during warm-up) and just
be ON all the time.  The "Main" pump would be controlled by
coolant temperature exiting the block enroute to the radiators.
It would not have to be as big as if it was the only one.
Just a theory .... Jim S.