I thought Jay's experience of no change in temp was enough data.

I don't see how you can conclude anything from the fact that the temperature
gauge reads the same.

If the oil cooler is working properly, it should keep the oil at a
steady-state temperature. In order to achieve that steady-state, it my have
to work much harder (I.E.: The thermostat may have to keep more oil flowing
through the cooler in order to maintain that steady temperature.) with less
oil on board to provide cooling.

This seems intuitive, but I honestly don't know enough about thermal
dynamics and engine design to conclusively say anything one way or the
other.

What we're not able to measure is how much "easier" it is for the engine to
remain at the a relatively cool 180 degrees, now that I've got 12 quarts
flowing through it instead of only 8.

I suppose the way to prove (or disprove) this theory would be to push the
engine to the limit, first with 8 and then with 12 quarts of oil on board,
and see if it overheats more quickly with less oil on board.

I suggest we try that with one of *your* engines first...

;-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"