I have to put my 2.5 cents (with inflation) about thermostats.
A thermostat is designed to get an engine above the thermostat setting quickly and to keep it there. The radiator keeps the engine cool. This is not a function of the thermostat. If you have excess cooling capacity in the radiator, the engine should run close to the thermostat temperature. The thermostat keeps the temp above its set point and the radiator has the capacity to drop the temp below that point so it should cycle around the thermostat temp.
However, if the engine puts out more heat than the radiator can transfer to the environment then the temperature will increase until the heat produced is balanced by the heat shed.
Note that as the radiator gets hotter relative to the environment (air temp) the heat transfer becomes more effective since the rate of heat transfer is proportional to the temperature difference. Conversely as the air temp gets hotter (Arizona in the Summer) the effectiveness of the radiator decreases because the temperature difference is less.
Heat is generated in the engine and is transferred to the coolant which is shed through the radiator. It is the temp in the engine that we care about and there are two transfer locations; the heads/block and the radiator. Really three locations since in the radiator the heat is transferred to the radiator metal which is then transferred to the air. All of the transfer locations need to work effectively for a good cooling system. If you have poor heat transfer in the heads/block to the coolant you risk pre-detonation and potentially other issues regardless of how well the other parts work.
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Fred Joslin
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