A car can run without a thermostat. However, operating a vehicle without a thermostat may result in serious engine damage caused by the engine operating at too high a temperature.
The car engine is designed to operate between 90 and 110 degrees Celsius. When the engine runs at the specified temperatures, parts such as the piston sleeve expand for optimal performance.
Without a thermostat, a car engine may not reach the appropriate temperatures, especially during the cold winter months. If the engine does not heat to at least 90 degrees Celsius, driving the vehicle wears down the parts faster. If the engine operates at temperatures over 110 degrees Celsius, the engine should be okay as long there is plenty of lubrication. Without an ample amount of lubrication, the engine runs the risk of overheating.