[CHANMADD]

It seems that a lot of folks have problems understanding the cooling system!!
The reason that a thermostat is installed is so that the engine can be kept at the best (most efficient for combustion) temp, without boiling over. 190 degrees to 200 degrees seems to be a nice temp to run at and is maintainable without to much hardware.
The thermostats job is to keep the coolant in the engine block ,and heads, until it is at max operating temp.Then the thermostat opens lets enough hot coolant out and into the radiator where it can be cooled. At the same time from the bottom of the radiator (Cold side) cool coolant is allowed into the engine to....Cool it down.
If the thermostat opens too soon, IE a lower temp, Then because the coolant is most always above that temp , the thermostat remains open all the time,so that the net effect is the same as having no thermostat. The coolant is flowwing as fast as the water pump is pumping. The coolant then does not stay in the radiator long enough to be cooled and returns to the engine still hot.
So if you want your engine to run at 190-200 put a 190 thermostsat in and keep a low pressure radiator cap.I like to run no more than a 13 pound cap ,less pressure to blow out seals and gaskets and hoses etc!!
John