Should I or Shouldn't replace t-stat ???

Well I tested the coolant with a candy therometer after she idled for 10 minutes and she was running @178. My factory gauge read 180 but my AutoLite gauge read 190. Guess the ole' 48 year gauge with no numbers is more accurate then the 7 year old name brand gauge, go figure huh. I put it better accuracy, guess I was wrong.