If your cooling system is running at 200 degrees with a 160 thermostat, you're producing too much heat and/or your cooling system is at it's capacity. You should have more cooling system than your engine requires so the thermostat can do it's job. Also, if your system is running at 200 degrees, what's the point of the 160 thermostat? Why not run a 180 or 195? Once the thermostat is wide open, it's not going to make it run any hotter.
