Finally resolved! Rearanger, you were on the right track, although we didn't fix it ourselves. I think Grandpa (my Dad) got tired of standing over a hot engine in 95+ degree heat with his son and grandson, guessing at what the problem might be! He finally said, "Take it to a shop and I'll pay". The shop found the Engine Temp Sensor was bad. Repair was only $92, including tax, so not bad. Thanks, Rearanger, for all the time you spent helping us. Much appreciated.