What Causes the Passat's Cooling Fan to Keep Running?
3 Answers
The Passat's cooling fan may keep running due to a damaged thermal switch on the engine radiator, a power failure in the low-voltage live wire of the thermal switch connector, a damaged high-pressure switch on the air conditioning pipeline, or a faulty fan. It is necessary to visit a 4S shop to inspect the specific cause and carry out repairs. Steel Radiators: In this type of radiator, based on its material and performance, it can be further divided into plate-type and column-type. However, when purchasing such radiators, safety issues should be taken into consideration. After all, they are used in automobiles, and poor-quality products can pose significant safety risks, posing threats to both the vehicle and its occupants. To test the radiator's anti-corrosion performance, it is essential to conduct a waterway inspection and not blindly trust exaggerated claims from sellers. Iron and Aluminum Radiators: In previous years, these two types of radiators were relatively widely used. However, due to their numerous performance drawbacks and less obvious advantages compared to steel radiators, they have now been replaced by steel radiators. It is rare to find these two types of radiators on the market today.
As a veteran mechanic with 20 years of experience, I've dealt with numerous cases of the Passat's radiator fan running continuously. The most common causes are a fan relay stuck in the ON position, causing the fan to run non-stop; a faulty coolant temperature sensor can make the car mistakenly think the engine is overheating, leading to constant fan operation; there might be a short circuit in the wiring, allowing current to flow directly to the fan and keeping it on; low coolant levels can trigger the system to sense high temperatures and cause the fan to run excessively; and a malfunctioning fan control module might directly command the fan to spin. My first recommendation is to check the coolant reservoir to ensure the level is within the marked range—top it up with water or antifreeze if low. If the coolant level is normal, proceed to inspect the relay for sticking or test the sensor for erratic signals. Leaving this issue unresolved can drain the battery, potentially leaving you stranded mid-drive and causing unnecessary hassle in daily life.
Our family has been driving a Passat for seven or eight years. Last year, the fan suddenly wouldn’t stop running, especially buzzing loudly after parking in the summer. At first, I thought it was normal due to high temperatures, but later I found that the coolant level had dropped significantly, causing the system to overheat and the fan to keep running. After consulting a mechanic, he said it’s also common for the temperature control switch to fail, making the fan think it’s in a high-temperature state. A faulty relay or poor wiring contact could also be the cause. If you want to DIY, you can first visually check if the coolant level is low and top it up or look for leaks. Then, pop the hood and listen for a clicking sound from the fan relay—if you hear it, the relay is likely stuck and needs replacing. Ignoring the issue could lead to the fan draining the battery, making it hard to start the next morning, or even causing the engine temperature to spike dangerously on the highway, risking an accident. So, I advise fellow car owners to promptly check simple components if they notice unusual noises and not take it lightly.
