1967 318 Barracuda running hot...

I had a 318 fury years ago that always ran over half on the temp gauge. It ran like a champ, but running over half bothered me. So I checked the T stat. 195. So I put in a 160. She made 20 miles and started getting hotter and hotter so time for a 180 T stat, she made about 50 miles b4 getting hot. Went back to a 195, no more problems other than the gauge reading over half. I fixed that by pulling the cluster and tweeking the needle of the temp gauge. Kim