You can’t trust thermostat ratings

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.