[nUcLeArEnVoY]

^^^ Lemme reword that. It helps act as a RESTRICTION, which helps aid in maintaining pressure.

And I really don't understand what's hard to interpret about what I said. I'm basically validating the point you made in your post prior to your replies to mine. A cooling system that is efficient and has enough capacity to actually maintain the thermostat's temperature setting will maintain it in closed loop operation (the modulating thing you're talking about). If it's not up to snuff, then the engine temp will be higher than the thermostat rating, meaning the thermostat will always be open as it tries to lower the temperature, but it cannot. This is like not having a thermostat. At that point, whatever temp the car runs at is what the cooling system is capable of maintaining on its own. Every engine is going to run at its own unique, inherent temperature. Compression ratio; power output; water jacket and passage design; ignition timing; valve timing; and fuel mixture all play a role in the temperature an engine will inherently run given. If you have a very good, or at the very least, SUFFICIENT cooling system, then yes, the thermostat will be able to regulate the temperature at or near the thermostat temperature by opening and closing in closed loop operation. However, if your cooling system doesn't have the capacity to allow the thermostat to keep control, your temps will run away and either overheat, or stop at a higher temperature than the thermostat that the engine inherently "likes."