What does the tension pulley do?
A drive belt tensioner is a pulley mounted on a spring system or adjustable pivot point that is employed to keep tension on the engine belts. … Both are used to keeptension on the engine serpentine belts in order that they can travel the many engine accessories.

How do you adjust a tensioner pulley?
Turn the adjustment bolt on the side, top or bottom level of the pulley counterclockwise with the ratchet and socket before equipment belt is loose enough to remove. Tighten the tensioner pulley by turning the adjustment bolt clockwise with the ratchet and socket until the belt is tight.
How do you know

A tensioner pulley courses the belt around the tensioner and allows the belt to spin while the tensioner maintains pressure against it. A failing tensioner pulley could cause power loss and harm to your belt-driven devices. You might have a failing tensioner pulley if you hear any squeaking or squealing beneath the hood. Bearings on the pulley can wear out, causing noise and temperature. Pulleys are usually made of either plastic or metal, so check the pulley itself for just about any damage as well. At O’Reilly Auto Parts, we have tensioner pulleys designed for many vehicle models.

The programmed pulley tensioner has an internal spring-loaded mechanism that keeps the serpentine belt under frequent tension. Its design allows it to keep the serpentine belt taut, in order that the other item pulleys rotate at the same rpm (revolutions per minute) while beneath the same safe pressure. Tensioner pulleys can also absorb slight shock loads that happen when the air conditioner cuts on and off. As a regularly rotating element, the pulley tensioner can give off some indicators before failure.

Rust and Corrosion
The pulley tensioner sits exposed to the elements at the front of the engine. Put through puddled water “splash-up,” with time the tensioner arm and pulley system can rust. Rust can freeze the automated tensioner device or rot the shaft bearings, that may cause a frozen situation in the adjustment pressure. Without the proper stress, the belt can slide.
Debris Contamination
Rocks, gravel and other road debris could be thrown up into the tensioner pulley grooves and jam the device. This can permit the serpentine belt to slip on the tensioner pulley and burn up. Overheated pulley temperatures results, and eventually the serpentine belt will melt and snap off.
Pulley Tensioner Spring
The pulley tensioner spring inside housing can become weak from age and repeated exposure to heat. This causes the belt to flutter and skip rather than maintaining a constant strain on the pulley. Symptoms of a poor spring present as glazing on the underside of the serpentine belt, with an occasional flickering of the dashboard’s charging light indicator. Squealing or squeaking will end up being listened to at the belt site.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, this means the inside shaft bearings have worn. This will cause a pulley misalignment. Negative bearings trigger an audible growling noise. The outer ends of the serpentine belt will fray and extend the belt. Gradually the rubberized belt grooves flatten out and trigger key slippage. An excessively wobbling pulley can throw the belt off, leading to all the components to quit functioning.
Lever Arm Freeplay
Some tensioner pulleys have markings on the casing that indicate the utmost range that the pulley can travel. If the lever arm of the tensioner rides under or higher the designated mark, this implies a stretched belt or a lever arm that has jammed in a single position.
Pulley Misaligment
The tensioner pulley face must match to the other accessory pulleys with a parallel alignment. Placing an extended, straightedge ruler against the face of the tensioner pulley, and then flushing it against another equipment pulley, can gauge the angle. Any off-angle measurement indicates donned shaft bearings in the pulley housing.
Serpentine Belt Noise
A moderately donned serpentine belt gives off a constant squeaking sound during engine idle. Belts that have worn severely task a loud chirping or squealing appear. The cause things to a glazed, worn or cracked belt. Dried out or partially frozen tensioner pulley bearings can cause such sounds by wearing out the belt prematurely.
Lever Arm Oscillation
A lever arm that repeatedly oscillates back and forth during idle or higher speeds means the the inside damper mechanism in the tensioner pulley has weakened or broken. This triggers sporadic tension strain on the belt and will manifest itself with intermittent chirping noises.