I disagree. The warm-up part of it's function is important....sure.....but the regulation of water flow is more important and the main function of the part. A thermostat will close while the engine is running if the heat produced in the engine is less than what the cooling system is shedding. Take going down a long hill, the engine is producing very little heat but the cooling system is still dumping heat. Once the coolant has lost enough heat, the thermostat will close at it's built in temp and restrict the water flow so the engine operation temp stays up where it should be. Once you hit the bottom of the hill, you'll step on the gas and produce more heat and the thermostat will open again and allow more flow so the radiator can shed more heat. This assumes all the components are working correctly and there are no internal engine problems (like thin cylinder walls) that can overwhelm the system. Running an engine with a 195 stat is fine.....for the engine. It's everything else in the engine compartment that's taking the hit. At 180, It's still running efficiently and easier on everything else. At 160, it's just not hot enough for mileage, power, heater performance, or anything else.
