Posted for "Christopher Zavatson" <Christopher.Zavatson@udlp.com>:

Bob,
I once heard from a Piper rep that the minimum oil quantity was based on max allowable oil consumption multiplied by the typical max endurance of a GA airplane.  Some of the max allowable oil consumption numbers are scarey ~1 qt./hr. I didn't confirm that with Lycoming, but it makes sense.

The sump acts like a settling chamber and deareation tank for the oil before the pump sends it back through the engine.  I doubt you would see a temperature change until the oil you are pulling into the pump contains significant amounts of air.  If you get down to this point your prop governor will probably also let you know.
Chris Zavatson
N91CZ