What is the reason for the fan running continuously when the water temperature is not high?
4 Answers
The reasons for the fan running continuously when the water temperature is not high are: 1. Failure of the cooling fan assembly or the cooling fan circuit; 2. The impeller of the engine water pump is detached from the shaft or the water pump is damaged; 3. Faulty water temperature sensor. Solutions for the fan running continuously when the water temperature is not high: 1. Inspect the fan circuit; 2. Replace the water pump and water temperature sensor. Reasons for the engine water temperature rising include: 1. Leakage in the cooling system or insufficient coolant; 2. Malfunction of the water temperature gauge; 3. Excessive scale in the cooling system, leading to poor heat dissipation; 4. Loose or broken water pump or fan belt; 5. The engine operating under prolonged overload conditions.
Last time my own car had this weird issue too, the temperature gauge showed normal but the fan kept running nonstop. I figured it might be the thermostat switch stuck closed—this component normally completes the circuit to activate the fan only when coolant temperature rises. Another possibility was a wiring short circuit, as aging wiring in older cars can easily trigger false activations like this. If the fan relay contacts get welded together, it’ll also cause the fan to run continuously—I actually replaced this part on my old car. Oh, and remember that the fan should run when the AC is on, but if it keeps spinning after the compressor shuts off, that’s abnormal. The trickiest scenario is poor coolant circulation—localized overheating due to airlocks in the radiator or a failing water pump can fool the sensor. I eventually fixed it by replacing the thermostat switch, saving hundreds in labor costs. Small car issues really shouldn’t be ignored—the sooner you diagnose them, the more money you’ll save.
Over the years I've worked on cars, this issue has been common. When the fan keeps running but the coolant temperature is normal, it's usually a control circuit malfunction. The thermostat switch acts like a gatekeeper - it only activates the fan when coolant reaches the proper temperature. If it fails, the fan works overtime. Wiring issues are another culprit - a short circuit in the grounding wire can directly power the fan. Burnt or stuck relay contacts are also frequent offenders, forcing the fan to run 24/7. Sometimes leaving the AC improperly shut off can trigger the fan too, though some vehicles are designed this way. Use a diagnostic tool to check real-time coolant temperature data - the gauge reading isn't always accurate as localized overheating may occur. Don't just look at surface symptoms - inspecting coolant flow and partial radiator blockages is practical. Address this promptly - running the fan motor continuously isn't cheap to replace.
My little white car had the same issue recently. The temperature gauge was at the midpoint, but the fan kept running nonstop. I asked an experienced driver, who said it's most likely a faulty thermostat switch - this component detects coolant temperature and controls the fan operation. It could also be a relay stuck in the ON position, just like a light switch that gets jammed and won't turn off. Another possibility is a short circuit in the radiator temperature sensor wiring, sending false signals directly to the fan. If you've just used the AC, pay attention - some vehicles need a few minutes before the fan stops. Also check if the coolant level is sufficient, as poor circulation can trigger false alarms. Get it to a repair shop early to scan for trouble codes with the diagnostic computer, before you end up burning out the electric fan.
