Normal temperature gauge reading?

I have a 1981 Toyota Celica with 180,000 miles. The radiator just exploded and I had it replaced along with the thermostat, hoses, gasket, cap. Went to get it, and the temperature gauge rises to the halfway point after just a few minutes. In the 16 years I've owned the car, the gauge normally rose to, and sat at, about 1/8th the way up, unless I was going up a very steep hill or it was a super hot day (if both, it sometimes inched up close to the red zone).

I expresed concern to the mechanic, so he exchanged the new 195 thermostat (recommended by the manual, I think) with a new 180 thermostat. The gauge went a little lower, but it's still at about the halfway point.

He insists that halfway is normal, and that my low gauge before was due to the thermostat being stuck open (for the last 16 years). Is that possible?

Thanks in advance for your help!