The thermostat rating is the temperature of which it is fully opened. The thermostat starts opening a lot sooner but it's not fully open until the rated temperature. Fact.
You can take a 180 thermostat n put it in a pot of water on a lit stove..and with a thermometer in it you'll see it starts opening about 150 degrees.
We learned that in HS auto shop class.
2 types of thermostats. Graduated and reverse poppet. Graduated are fully opened at 180, and poppet style start to open at 180. Quick open quick close. Poppet style typically cycle open and closed.
