Percolation? Heat soak? Don't drive during summer??

The thermostat does not control the highest temperature your engine will see. Just the opposite. It controls the lowest temperature it will see. The 180° thermostat opens at about 180 and stays open as long as the water stays above 180°. If the temperature goes someplace below 180°, the thermostat will start to close. The idea is to keep the engine above 180° at all times. How high it goes above 180° depends on how screwed up the engine and/or the cooling system is. But your highest temperature is not controlled by the thermostat.