A thermostat's job is to regulate temperature. Below it's temperature it will be closed. As temperature rises it opens just enough to allow coolant to flow to the radiator. If it ever reaches wide open it's because it's asking the radiator for more cooling and the radiator is returning all it can. This scenario should never be seen, if it is you need more cooling, like a bigger radiator.


69 Super Bee, 93 Mustang LX, 04 Allure Super