A faulty car thermostat is bad news. Without a properly functioning thermostat, your engine cannot maintain the optimum temperature: a cause of much misery. But how do you recognize problems with the thermostat? In this article, you can read all about the symptoms of a broken car thermostat. The temperature of the motor can vary greatly. The outside temperature, the speed at which you drive and how heavily the engine is loaded, among other things, means that that temperature can fluctuate considerably.