What Causes the Car Radiator Fan to Keep Running?

[DeLeo]

Reasons why the car radiator fan keeps running: 1. High water temperature in the radiator after the engine is turned off, causing the cooling fan to operate for a while before stopping; 2. Malfunction of the cooling fan; 3. Short circuit in the cooling fan's wiring. The car radiator is a key component in the vehicle's cooling system, and its function is to dissipate heat. The coolant absorbs heat in the water jacket, flows to the radiator to release the heat, and then returns to the water jacket for circulation, achieving temperature regulation. How the car radiator works: When the engine's water temperature is high, the water pump circulates the coolant repeatedly to lower the engine's temperature, protecting the engine. In winter, if the water temperature is too low, the circulation stops to prevent the engine from becoming too cold.

[SanLukas]

I've encountered this issue before, and there are quite a few common causes when repairing cars. The most likely culprit is a faulty coolant temperature sensor, which is installed between the engine and the radiator. If the readings are inaccurate, the fan will keep spinning like crazy. Don't panic if the fan goes wild after turning on the AC in summer, but it's not normal if it doesn't stop after turning off the AC. A stuck relay is also a hidden killer—my old car had this problem when the relay contacts were burnt and stuck together, continuing to work even after power was cut. A short circuit due to grounding is even more troublesome, requiring a check for damaged insulation on the wiring. The most easily overlooked issue is a stuck thermostat—my neighbor's car had this problem, where the coolant circulation was blocked, causing the fan to spin wildly to dissipate heat. If the fan itself has an internal short circuit, it won't stop either. By the way, don't push your luck—a constantly running fan drains the battery heavily. I had to jump-start someone's car twice last month because of this.

[SanGage]

Yesterday when I was fixing that car, the fan just wouldn't stop running. Using the diagnostic tool to read the data showed the coolant temperature was falsely high. The key components to check are the coolant temperature sensor and thermostat - these two buddies control the cooling rhythm. I found the sensor connector was oxidized when I unplugged it, but after sanding it down and plugging it back in, everything worked normally. If the fan keeps running after idling for 20 minutes, there's definitely a problem. Actually, you can judge by feeling the radiator hose temperature: if it's cold, it means the thermostat isn't opening; if it's hot but the fan keeps running, then check the electrical circuit. Last week I met a skilled Touareg owner who fixed it by simply unplugging and replugging the fan relay a few times, but I'd advise regular car owners not to randomly pull fuses.

[VonAngelina]

Actually, the fan spinning wildly is the engine crying for help. In the closed-loop control of the cooling system, the temperature sensor, ECU, and fan are in a battle. If the sensor falsely reports a high-temperature signal, the ECU commands the fan to work at full capacity. Once, after cleaning the throttle body, my fan acted abnormally, and it turned out that the wiring harness of the coolant temperature sensor was crushed when unplugging the connector. Nowadays, new cars are more complex, and it might be the body control module malfunctioning and giving wrong commands. I once fixed a Peugeot 307 with a burnt-out electric fan module, and replacing the module immediately solved the problem. Low coolant levels can also cause overheating, but in such cases, the fan spinning is a normal protective mechanism.