This is kinda fun. I do understand the difference between a thermostat and a heat exchanger. All I'm saying is that the thermostat can and does regulate the temperature of the water. Engine thermostats gradually open, and how much they open is dependent on the coolant temperature. This allows for a feedback mechanism to control water temperature by controlling the rate at which water circulates through the system.

Both of you are right. I am no teacher or engineer but I did just cover this in school.

I decided to run the car without it and I too was worried about the car not running right because it wouldnt reach operating temps with out the thermostat but its fine.

It takes longer for the car to warm up obviously but thats it still sits at operating temp later.

An automotive wet thermostat by itself cannot regulate temperature. it will regulate flow to a certain degree based on the heat of the coolant (as you said, various degrees of opening). It does not depend on any electrical values to operate, unlike a home heat and air thermostat. It depends wholly on heat to actuate. It is part of a synergistic system whose duty is to manage heat on a whole.

You will agree that the overall manager is the EMS, and it gets feed from the sensors, in this case the water temp signal to the EMS, right? From the temp signal, it will determine fan speed, enter the temp value into the equation to determine whether to run rich or lean out (engine runs richer when cold), idle high or low, etc.

Circulation. Even by itself, the EMS is not going to control the rate of circulation in this car, unless you have an electric water pump that is a variable speed type that takes input from the EMS based on some pre-determined values. In the case of our car, we have the traditional belt-driven variety, and the speed governor for this is your right foot.

In closing, the cooling system is completely synergistic. It depends on the thermostat, water pump, radiator, cooling fan(s), sensor and EMS to work properly. Not one item completely regulates the entire cooling system. In fact none of them do on their own.

Running with no thermostat may cause your engine temps to be higher. Coolant moving through the engine too quickly will not absorb the heat from the cylinders efficiently. Your gauge will display a lower coolant temp but the cylinder temps will actually be higher.

I stand corrected mrfred, partially The thermostat is the major regulator of engine cooling, as you have stated, and the engineers who design the engine depend on it to allow the engine to warm up to a pre-determined value that is deemed an engine's thermal efficiency, and from that point it's all engine management system doing its job of monitoring values and calculating variables to maintain the engine's overall efficiency, which we're all so fond to disrupt with go-fast bits that upset the balance.

Sometimes I get lost in the woods...