What are the reasons for the loud fan noise in BMW e90 engine?
3 Answers
BMW e90 engine fan noise may be caused by the following reasons: Possible excessive bearing wear: Inspect the radiator and surrounding components to check for excessive bearing wear. If damaged, simply replace the bearing. Examine whether the cooling fan blades are rubbing against anything. If not, the fan is likely damaged, and replacing the fan bearing or coupler should resolve the issue. Poor fan cooling performance: This may be related to the fan belt or blade balance issues, or possibly due to a dirty radiator causing poor heat dissipation, which affects air intake volume. This leads to increased electronic fan speed and consequently louder wind noise. This problem does not affect daily usage. Clean the radiator and fan blades, and check for loose fan mounting screws. If the issue persists, directly replace the car's cooling fan.
My BMW E90 also had the issue of loud fan noise before, and it took me a long time to figure it out. This situation is mostly caused by a problem in the cooling system, such as the radiator being clogged with dust or poor coolant circulation, forcing the fan to ramp up its speed to cool things down. It could also be due to aging fan bearings, making a squeaky noise when spinning. The problem is most noticeable when using the AC in summer because the compressor generates additional heat. I recommend first checking the coolant level and whether the front radiator fins are clean. If that doesn’t help, you might need to measure the fan motor bearing clearance. Don’t ignore it—if the fan fails completely, the engine could overheat and stall. I had this happen on the highway once, and it was terrifying.
As a mechanic who frequently works on European cars, I've encountered many cases of noisy E90 fans. The most common issue is reduced cooling system efficiency, which forces the fan to operate at full speed, creating a roaring sound. If you open the hood and find the gaps between the condenser and radiator clogged with poplar catkins or insect remains, this is likely the cause. Additionally, unstable rotation due to worn carbon brushes in the fan motor can also cause abnormal noises. Just last week, I replaced an entire fan assembly due to this noise issue. Another less common reason: the engine control unit misinterprets high-temperature signals, causing the fan to spin wildly. A simple solution is to use a diagnostic tool to read the coolant temperature sensor data stream, which is much more accurate than the temperature gauge.
