There are a number of signs of impending tensioner failure. A failing tensioner can damage a newly replaced belt, cause a belt to squeal or break, or merely be mistaken for belt squeal.
Technicians should be advised to pay attention to some signs that a tensioner may be failing. They should always take care that the engine is off when attempting to manually rotate a tensioner, and be extra careful when listening for noise while the engine is running.
All of the symptoms below should be taken as a sign that a tensioner may be in need of replacement.
Tensioner Noise: Any squeaks or rattles are indications of impending failure.
Idler Bearing Wear: Noise or resistance when turning the pulley with the belt removed could indicate bearing failure.
Rust Bleed: Trapped dirt and grit will wear away the rust inhibitors from flat spring tensioners. Over time, rust can bleed from the tensioner between the arm and the base, and affect other electrical components such as the alternator. Cracks: Check for damage to the arm, housing, or bracket. Cracks most commonly occur at the tension stops and mounting bolts. Tensioner Arm Misalignment: This may appear as metal-to-metal contact between the arm and spring housing, and will be indicated by shiny, smooth streaks or gouges in the metal.
Pulley Wear: Serpentine drive pulleys are made from either plastic or steel, and can have a flat or grooved surface. Although the pulley itself can be replaced, these signs indicate other problems, which could mean the entire tensioner should be replaced.
Sticky or Uneven Tensioner Arm Movement: It should move smoothly and freely. If it binds, catches, or moves in segments, the tensioner should be replaced.
Loss of Spring Force: There should be resistance to this movement. If there is none, the spring has lost its force. Other indicators are belt squeal from slippage, or loss of rotation of a belt-driven component.
Improper Belt Tracking: If the belt is not properly tracking in the centre of the pulley, the tensioner could be misaligned and may be in need of replacement if this is the result of bent or worn components. Source: Gates Corporation