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

How do you change a tensioner pulley?
Switch the adjustment bolt on the side, top or bottom level of the pulley counterclockwise with the ratchet and socket before accessory 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 guides the belt around the tensioner and allows the belt to spin as the tensioner maintains pressure against it. A failing tensioner pulley could cause power reduction and damage to your belt-driven systems. You could 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 heat. Pulleys are usually made of either plastic or metal, so check the pulley itself for just about any damage as well. At O’Reilly Car Parts, we’ve tensioner pulleys available for many vehicle models.

The automatic pulley tensioner has an internal spring-loaded mechanism that keeps the serpentine belt under constant tension. Its design allows it to keep the serpentine belt taut, to ensure that the other accessory pulleys rotate at the same rpm (revolutions each and every minute) while beneath the same safe pressure. Tensioner pulleys can also absorb moderate shock loads that happen when the air conditioning unit cuts on and off. As a continuously rotating part, the pulley tensioner can give off some warning signs before failure.

Rust and Corrosion
The pulley tensioner sits subjected to the elements at the front end of the engine. Subjected to puddled water “splash-up,” as time passes the tensioner arm and pulley device can rust. Rust can freeze the computerized tensioner device or corrode the shaft bearings, that will cause a frozen placement in the adjustment pressure. Without the proper tension, the belt can slip.
Debris Contamination
Rocks, gravel and other road debris can be thrown up into the tensioner pulley grooves and jam the device. This can allow the serpentine belt to slide on the tensioner pulley and melt away. Overheated pulley temperatures results, and finally the serpentine belt will melt and snap off.
Pulley Tensioner Spring
The pulley tensioner spring within the housing can become weak from age and repeated contact with heat. This triggers the belt to flutter and skip rather than maintaining a constant pressure on the pulley. Symptoms of a weak spring demonstrate as glazing on the lower of the serpentine belt, with an intermittent flickering of the dashboard’s charging mild indicator. Squealing or squeaking will always be heard at the belt site.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, this means the interior 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 stretch the belt. Finally the rubber belt grooves flatten out and cause main slippage. An excessively wobbling pulley can throw the belt off, creating all the components to quit functioning.
Lever Arm Freeplay
Some tensioner pulleys possess markings on the housing that indicate the utmost selection that the pulley can travel. If the lever arm of the tensioner rides under or higher the designated mark, it indicates a stretched belt or a lever arm which has jammed in a single position.
Pulley Misaligment
The tensioner pulley face must match up to the other accessory pulleys with a parallel alignment. Placing an extended, straightedge ruler against the facial skin of the tensioner pulley, and flushing it against another item pulley, can gauge the angle. Any off-angle measurement indicates put on shaft bearings in the pulley casing.
Serpentine Belt Noise
A moderately worn serpentine belt gives off a constant squeaking noise during engine idle. Belts which have worn severely project a loud chirping or squealing sound. The cause things to a glazed, put on or cracked belt. Dry or partially frozen tensioner pulley bearings can cause such sounds by deteriorating the belt prematurely.
Lever Arm Oscillation
A lever arm that repeatedly oscillates back and forth during idle or more speeds means the the inside damper mechanism in the tensioner pulley has weakened or broken. This causes sporadic tension pressure on the belt and will manifest itself with intermittent chirping noises.