I changed out my 180 for a 195 because it'* winter in Florida and my mileage went down about 2 mpg. Now after the engine gets up to temp, the temp gauge will unpredicatably move between about 210 and 160 in less than 10 seconds. With the 180, the temp gauge was steady once the engine warmed up unless I was stuck not moving in traffic. There'* no change in the heater output temp when this happens.
I'm pretty sure I didn't leave any major air in the system, and it should purge itself anyway. Changing the thermostat was the only thing done at that time. Thoughts, ideas?