I always use a 180 degree. I also always drill one 3/16 hole in the outer parimeter to act as a air bleed hole. Something I've learned over the years, and it was a hard lesson is never buy 1 thermostat. Buy three.
I've bought the ones that cost $10 and they didn't work correctly, and I've bought the ones that cost $2 and they didn't work correctly. Why I buy three is because usually one out of the three is good. I learned to check them in boiling water to check the correct opening point and then let them cool to check the closing point. If one is good out of the three I take the other two back to the store. Years ago in my Cutlass around town, it would run a solid 190. If I got on the interstate, it would creep up to 210, 220, and sometimes up to 230 if it was real hot outside and I didn't like that. I couldn't figure out why it did that. Finally I tested the Stat which was not very old and it opened at the correct temp, but it wouldn't close until the water had almost gotten completely cooled. So I went to the parts store and bought three new ones and tested each one. The first wouldn't open until it got to around 240. Bad. The next opened and closed as it should so I put it aside. The last one would open but wouldn't close so I took the two bad ones back and told the guy behind the counter they were bum. Odds he sent them back? Doubtful, Odds he put them back on the shelf for the next sucker? Real good. I agree with the rest of the guys as well, throw the flex fan away.