Coolant flow

It might be surprising, but thermostats are controlled by a small pellet of wax trapped between a piston and cylinder. The opening point of the thermostat is the melting point of the wax. The thermostat design takes advantage of the change in volume of the wax going from a solid to a liquid. Wax expands by 17% upon melting which pushes the piston open. This happens over a 1-2°F range. Thus, there is no way that a thermostat will open over a 10-20°F range. I produced this type of wax using a synthetic process and know how this product is produced.