Found this info very interesting, thought I'd share.
The thermostat is much maligned, often misunderstood, and seldom credited for its mostly reliable service.
Thermostats in proper working order, control only the minimum operating temperature at which engine coolant is allowed to heat. A properly operating thermostat has absolutely nothing to do with how hot the engine becomes. If you are experiencing an over heating engine, changing to a colder thermostat will not correct the condition, it only allows the coolant more time to over heat. A thermostat once fully open can do no more to control temperature. The overheating cause lays somewhere else.
Some believe that removing the thermostat completely can remedy over heating concerns. This can be deceiving, with out some flow control coolant can pass through the radiator without slowing enough to cool, returning to the engine hotter with each circuit of the liquid.
The temperature stamped or marked on the thermostat is the "start to open" rating. This is often referred to as when the thermostat just "cracks open" and allows some coolant to flow. This is in contrast to the popular belief that the temperature specification identifies when the thermostat is fully open. Most applications have a thermostat that is designed to "crack" at about 180 to 195 degrees F. If the thermostat opening is set too low or too high engine damage can be the result. High coolant temperatures can cause abnormal combustion, loss of power, damage to bearings and other moving parts, etc. Low engine operating temperatures lead to excessive fuel consumption, dilution of lubricating oil by the addition of unburned fuel, the formation of sludge from the condensation of water in the crankcase along with a host of other concerns.
Most thermostats are designed to be fully open 20 degrees F after cracking. So 215' on a 195' would be considered "Normal"
