Thermostats do not regulate engine operating temperature. Your engine is going to operate at whatever temperature it normally operates at regardless of the Thermostat rating.
Thermostats only regulate the amount of time it takes the engine to reach its normal operating temperature. A thermostat with a lower temp rating will open sooner allowing more water to flow through the radiator causing the engine to take longer to reach the operating temperature that it is used to running at.
It the winter, it will take longer for your heater to feel like it's working.
