In the front of your BMW’s engine you have what is called the serpentine belt system. This system is critical as it uses some of the rotational torque from your engine to run the electrical, cooling, and power steering systems. The power is generated from the large lowest pulley called the crank pulley and through pulley system and belts the electric generator, power steering pump, and water pump are spun. The belts are made out of reinforced rubber and are precisely measured to length to provide enough mechanical grip to spin the pulleys. If for any reason the serpentine belt were to slip off or break your BMW would lose electrical power, steering would become heavy, and if run your BMW long enough your engine could overheat. In short you’d need to pull over and call a tow truck.
How to keep your serpentine belt system in good shape?
Your BMW’s serpentine belt system can develop issues in a couple of ways. The belt being made out of rubber can dry crack with age. This will cause it to lose grip and eventually snap or shred to pieces if it is not changed on time.
The pulleys on the system spin on internally lubricated sealed bearings. Over many miles the bearing seals fail and the pulleys will start making a chattering or a consistent chirping noise. The chirping noise will be loudest a idle and go away when you rev the engine. When the bearing completely fails the pulley will seize and the belt will try to force the pulley to spin. This will cause the pulley to explode or the belt to shred potentially damaging other components in the area.
You can prevent this from happening by checking the belt and pulleys when you notice chattering or chirping noises when you start your car in the morning. The belt should be removed and checked for cracks on the tread. The pulleys should be manually spun and checked for smoothness and the right amount of resistance. A pulley with a bad bearing will feel gritty like sand got inside when you spin it by hand or it will spin freely with no slight resistance when the seal has failed and fluid leaked out. Either of these conditions will require replacement of the failing components to keep you system in good shape.
If you hear the classic bearing noise on cold starts, but don’t have the time or ability to check your belts and pulleys yourself we recommend you bring your German Automobile to a trusted shop like Bimmer Motors to have the problem diagnosed and addressed before a belt or pulley breaks and your car leaves you stranded.