After replacing the t.stat and purging the air out of the cooling system, make sure the water pump and the clutch fan is working properly. While re-checking for the concern, see if there is any presence of antifreeze coming out of the tail pipe IF the temp is still at 210-220*F . in the worst case scenario it's possible that it could be a leaking headgasket or a hairline crack in the cylinder head. Verify that the engine oil is not contaminated with coolant as well. Often, the Radiator cap is overlooked as the culprit but this symptom indicates a boil out thru the overflow reservoir.