A wide array of problems can arise from an improperly tensioned serpentine belt:
Understanding Why Tensioners and Belts Wear at the Same Time
What causes tensioners to wear?
Dirt and grime can get into tensioners, making the springs and dampers bind. Stop-and-go driving can cause varying engine loads which means irregular tension. An average tensioner will cycle 200 million times in its service life, adding to the general wear and tear.
What’s the best protection?
Because tensioners wear at the same rate as belts, the best way to make sure your accessory belt drive system will run at peak performance is to replace the tensioner with a new serpentine belt. To reduce belt warranty problems, comebacks and labor claims, Gates®
recommends that all Accessory Belt Drive System (ABDS) components, including the belt, tensioners, and pulleys, be replaced at the same time.
Understanding Belt & Tensioner Failure Modes