[marge1990]

What happens if you run a car with a lower temperature thermostat. For instance, instead of using a 195 degrees, I use a 160 degrees?

 

[MrShorty]

Obviously, the thermostat will open colder. Whether the engine will actually run cooler or not depends on the condition of the rest of the cooling system.

What year vehicle? I've seen a serious drop in gas mileage on some computer controlled vehicles. As the computer monitors engine temperature, it runs in a "warm up" mode until normal operating temperature is reached. During this "warm-up" mode, the computer is using a little bit different algorithm, which causes the engine to run less efficiently. If the thermostat opens too soon, and the engine never reaches a temperature that the computer deems "normal," the computer will always operate in "warm up" mode, and you can get a drop in gas mileage.

If this is an older, non-computer controlled vehicle, you may not see much if any difference, other than the running temperature.