[thom4782]

Someone said it earlier: the thermostat trigger point only effects when the radiators begin to affect the temperature of the circulating coolant.

If the thermostat is closed, the coolant temperature of the coolant rises because the heat input from the engine is far greater than the loss. Essentially engine generated heat is lost directly from the engine block into the surrounding air. This is a very inefficient heat exchange.

Once the thermostat opens, the rate of heat loss in the coolant increases because the radiator exposes a large surface area of hot coolant directly to the lower temperature of the surrounding outside air. The rate of heat loss increases even further when air flows over the radiator as the car moves forward and refreshes the air surrounding the radiator with cooler air. This is why cars have radiator fans which increase the rate of heat loss when stopped in traffic.

It may be in boxster engines that the balance point between heat in from the engine and heat out from the radiators is above 160. If this is the case, then the low temperature thermostat has little effect on lowering the temperature gauge reading. If it does have an effect on the gauge reading, you would most likely notice it on cold winter days when the heat loss from the radiators is much greater because of the temperature difference between the coolant and outside air is much greater than on summer days.

I experienced this personally in college one frigid winter day as I drove my MGC from Connecticut to Ohio. The temperature gauge read Cold for the first couple of hours until the outside temperature warmed up to 20F. Then the gauge started to move about 1/3 up the scale toward Hot. There was some heat in the car from the heater. Late that day when the sunset and the outside temperature fell below 0F, the gauge fell back to Cold and I froze when the heater only blew cold air.

So the main reason cars have thermostats IMHO is to make sure the engines get up to an efficient operating temperature regardless of how cold it is outside and to make sure the heater warms the inside of the car. The radiators and the fans keep the coolant temperature from getting too high so the engine suffers less heat fatigue and doesn't allow the coolant to vaporize in the worst case. BTW: the coolant can remain a liquid at temperatures above the boiling point of water mainly because the coolant system is pressurized.