Summer Update
The outdoor temps have changed dramatically from my post in March about "problem solved". Yesterday I was at the Hallett track for a drivers school, and the air temp was around 100F, with a heat index of around 107F. HOT!!!
The engine temp drifted from ~80C (with a 180F thermostat) up to about 90C (sorry, my gages are in C not F) after several laps, but nothing erratic. Yeah!!! The
oil temp normally stays within a few degrees of the water temp in moderate weather and when just driving around town. On the track, it got up to ~110C.
Pictures of my mods from March are located here:
Small Block Surge Tank???
Quick note: I made several changes back in March, so I don't know if just adding the surge tank was all that was necessary to tame my erratic temp. It may be that moving my water temp sensor, rerouting the heater hoses, and adding a bypass hose had a big part in the solution.
Thanks again to all that helped with suggestions.