Tensioner Pulley
The pulley mounted on the accessory belt tensioner assembly that guides and maintains tension on the serpentine belt.
A tensioner pulley is the rotating wheel component of an automatic or manual belt tensioner assembly. It sits flush against the serpentine belt, guiding its path and applying constant pressure to ensure the belt does not slip off the alternator, water pump, power steering, or A/C compressor pulleys.
The tensioner pulley consists of a steel or plastic wheel with a sealed ball bearing in its center. In an automatic tensioner system, the pulley is bolted to a spring-loaded arm that adjusts dynamically to belt stretch and engine load. In manual systems, the pulley is mounted to an adjustable bracket. The pulley can have a smooth surface (running on the back of the belt) or a grooved surface (running on the ribbed side of the belt).
Because the tensioner pulley spins constantly at high speeds, its internal bearing eventually wears out. As the grease inside the bearing dries up, the pulley will begin to make noise. A failing tensioner pulley produces a high-pitched squealing, chirping, or growling sound that gets louder as engine speed increases.
If the bearing fails completely, the pulley can seize or wobble, throwing the serpentine belt off the engine and causing a sudden loss of steering, cooling, and charging systems. Replacing a noisy tensioner pulley or the complete tensioner assembly is a routine preventive maintenance service.