If your car's fan clutch has gone awry, there are several ways to tell. For starters, your engine tends to run a bit hotter than usual or would outright overheat, especially when you're cruising at lower speeds or are idling. This is because the fan's clutch fails to engage the fans themselves, thus failing to force air through the radiator. In addition, another common symptom of a faulty fan clutch is having the engine run too cold. During wintertime, a bad fan clutch might run constantly (instead of intermittently), hence cooling the engine a bit too much. Besides that, you might notice how the radiator fans emit a lot of noise and vibration. So much so, that it could even force the fan blades to flex and shatter over time.