The new tstat is opening at 180* and coolant is flowing. The problem is that unless your moving alot or at highway speeds your not getting enough airflow to maintain that temp. Thats why you have cooling fans. They keep air moving even when your car is not. Now your engine computer turns those on around 210 ish degrees stock. This is pretty dang hot if you ask most people here so that why everyone gets the pcm set up to turn the fans on around 185. This would be bad by itself because without a 180* thermostat your fans would just be pushing air non stop against a radiator that isnt flowing any coolant because the 195 degree thermostat isnt letting the engine get that cold. Thats why you need both.
Recap:
Just a thermostat = cooler temps if theres enough airflow but otherwise not much changed.
Just a tune = fans running non stop
Tune + Thermostat = Happy 180 degree engine
