These coolant temperatures you have listed above, as well as the behavior of the observed coolant temp fluctuations, IMO are completely normal and I see similar patterns in my system.Okay, so I just replaced my thermostat (and other things) and the temps aren't right, although my heater is blowing super hot now, which it wasn't before.
Driving around town right now with the OAT at about 60-70F (no heat and no AC) the ultra gauge shows 185F for a while, but it keeps creeping up to about 188 and then will spike at 190-192 for brief periods but then go back down to 188. But what I noticed that's weird is that when I come home, I am going about 25mph up a hill and then let off the gas, turn right, and then go down a hill. When I do this the temp jumps to 192 almost immediately. VIDEO but then cools back down to 188.
Nothing to worry about.