What is the purpose of a thermostat?

[chopper]

Renaissance man:

Lyle and dalola are correct. The thermostat is there to maintain a minimum temperature. Another important function is to aid in helping the engine come up to temperature quickly after startup. The thermostat does this by restricting flow of the coolant through the radiator until the coolant in the engine heats up. Once the coolant temperature reaches the thermostat's setting, the thermostat begins to open and allow flow through the radiator. As the fluid is cooled through the radiator, the thermostat partially closes and regulates the temperature by providing a partial restriction to the fluid. Once it's fully open, additional elevation of the temperature will have no further effect on the thermostat or the coolant flow through the radiator. The coolant flow is then regulated as a "controlled leak" through the thermostat to maintain coolant temperature.

The thermostat also acts as a flow restrictor, and provides some back pressure to prevent cavitation of the coolant as it runs through the engine, especially through the cylinder heads. This is the theory behind Southern Automotive's advice to remove the thermostat and install a restrictor plate. I have heard some racers swear by this and others say the theory is unsupported. Since I figure Mr. Parham knows more about his engine than I do, I took his advice and left his restrictor plate installed.

As far as coolant temps go, 190 on the road and 210 at idle is, IMHO, certainly acceptable. As others have pointed out, many late-model cars run as high as 230 for efficiency and emissions. Higher than that would cause me concern.

JAM1775:

I am interested in your comment about running the engine at lower coolant temperature for more power. For point of discussion, I have seen graphs in some automotive texts which show engine wear as a function of sustained coolant temperature, and most show a marked increase in wear (as a function of component clearances) when the coolant operating temperature is stabilized at temperatures below 180 degrees. I can certainly understand why cooler cylinder heads would aid in power production (denser fuel/air mixture into the cylinder) but do you have an opinion about the increased wear issue? Or is the 20 degree difference not significant?