There's been several great discussions on engine cooling here.Some say the thermostat or restriction provides presurization of the cooling liquid in the block by the pump pushing against the restriction, eliminating steam pockets.Liquid can take on more heat than steam.Some say you should run an engine as hot as practical to increase efficiency ,Nascar engines engines run around 220 degrees for example.Of course, 220 degrees on a street engine is right on the edge, 190 gives a safety factor.
