[icingdeath88]

The coolant still needs to be flowing at all times, to prevent hot spots, and so the engine can warm up evenly, etc. In the factory configuration, when the coolant isn't flowing through the radiator, it's flowing through the various bypass lines. The T-stat really just changes the path of least resistance from the bypass lines to the radiator, but the coolant is still always flowing when the T-stat is "closed". It's just limited to flowing through the bypass lines, which keeps it from getting cooled down by the rad, until it warms up enough to open the T-stat.

That said, you can certainly adjust the speed of the pump to flow slower when the cooling demands are not so much, and higher when they are. But I don't think you would want it to ever fully stop.