What Are the Signs of a Bad Belt Tensioner?

by Scarlett Gauthier
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The belt tensioner is a crucial part of any engine. Its functions include tightening the engine belt and transferring power through pulleys from the serpentine belt to the alternator. It is responsible for generating the correct amounts of tension to allow the engine to run and drive its components. Belt tensioners lose their strength and efficiency over time, which can lead to an engine failure if the belts aren't replaced. It's helpful to know the signs that the tensioner is worn or needs replacement.

Battery Light

The car battery light will light up when the belt tensioner is failing. The battery will begin to run down due to the fact that the belt is slowing down and slipping out of its compartment. In addition, the alternator will no longer turn fast enough to power the battery.


One of the main signs that a belt tensioner needs replacement is the looseness of the belt. Listen for a fluttering" noise while driving or while the car is idling. This indicates the tensioner is too loose. Other noises such as squealing or whirling from the front of the engine mean the spring inside the tensioner is weakening. In this case, the belt tensioner needs to be replaced.

Rust and Debris

Rust or corrosion can build up around the tensioner, as well as dirt and mud. Rust prevents the tensioner from spinning freely, which can cause further damage to the engine. Corrosion can occur in areas with a colder climate, and where roads are heavily salted during winter. Rust also tends to distribute into other parts of the engine, including the alternator.

Pulley Damage

Any damage to the automatic tensioner pulley can cause damage to the belt tensioner due to the vibrations caused by the pulley. Physical damage to the pulley is an indication of extreme tension or physical interference.

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