Section 328 (Cooling System): Engine: Thermostat: Operation
WARNING: This page is about a different car, the 2019 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.
The wax pellet is located in a sealed container at the spring end of the thermostat. When heated, the pellet expands, overcoming closing spring tension and water pump pressure to force the valve to open.