The serpentine belt that drives the accessories on late model engines has an automatic tensioner that keeps the belt tight. Most people know the belts are a maintenance item and eventually have to be replaced. But many do not know the spring-loaded automatic tensioner that keeps a serpentine belt tight can also wear out or become weak. This can cause a variety of problems if the tensioner is not replaced when a new belt is installed.
The drive belt tension is made up of four main parts – the base, tensioner arm, spring and pulley. The base holds the other parts, and the spring keeps the belt pulled tight. The pulley is what facilitates movement of the belt. The tensioner arm is found on the bottom of the tensioner, and if you press on it, it will work against the spring, delivering enough slack so that you can adjust or remove the belt.
The automatic tensioner has a coil spring inside that applies just the right amount of force against the belt to keep it tight. The tensioner also provides a little "give" so it can absorb and cushion shock loads on the belt that occur when the A/C compressor clutch cycles on and off. What's more, the tensioner automatically compensates for wear and keeps the belt under constant tension.