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 being used to keeptension on the engine serpentine belts in order that they can travel the various engine accessories.

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

A tensioner pulley guides the belt around the tensioner and allows the belt to spin while the tensioner maintains pressure against it. A failing tensioner pulley can cause power damage and harm to your belt-driven devices. You may have a failing tensioner pulley if you hear any squeaking or squealing beneath the hood. Bearings on the pulley can degrade, causing noise and heating. Pulleys are usually manufactured from either plastic or steel, so examine the pulley itself for any damage aswell. At O’Reilly Auto Parts, we have tensioner pulleys designed for many vehicle models.

The automatic pulley tensioner comes with an internal spring-loaded mechanism that keeps the serpentine belt under continuous tension. Its design enables it to keep the serpentine belt taut, to ensure that the other equipment pulleys rotate at the same rpm (revolutions each and every minute) while under the same secure pressure. Tensioner pulleys can also absorb gentle shock loads that happen when the air conditioning unit cuts on and off. As a constantly rotating element, the pulley tensioner can provide off some indicators before failure.

Rust and Corrosion
The pulley tensioner sits exposed to the elements at the front of the engine. Subjected to puddled water “splash-up,” as time passes the tensioner arm and pulley system can rust. Rust can freeze the automated tensioner device or rot the shaft bearings, that will cause a frozen location in the adjustment pressure. Without the correct tension, the belt can slide.
Debris Contamination
Rocks, gravel and other highway debris could be thrown up in to the tensioner pulley grooves and jam the device. This can permit the serpentine belt to slide on the tensioner pulley and shed. Overheated pulley heat results, and finally the serpentine belt will melt and snap off.
Pulley Tensioner Spring
The pulley tensioner spring in 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 fragile spring display as glazing on the underside of the serpentine belt, with an intermittent flickering of the dashboard’s charging lumination indicator. Squealing or squeaking will be listened to at the belt site.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, it means the interior shaft bearings have worn. This may cause a pulley misalignment. Undesirable bearings trigger an audible growling sound. The outer ends of the serpentine belt will fray and extend the belt. Sooner or later the rubber belt grooves flatten out and trigger major slippage. An excessively wobbling pulley can toss the belt off, triggering all the accessories to quit functioning.
Lever Arm Freeplay
Some tensioner pulleys possess markings on the casing that indicate the utmost range that the pulley can travel. If the lever arm of the tensioner rides under or over the designated mark, it indicates a stretched belt or a lever arm that has jammed in one position.
Pulley Misaligment
The tensioner pulley face must match up to the other accessory pulleys with a parallel alignment. Placing a long, straightedge ruler against the facial skin of the tensioner pulley, and flushing it against another equipment pulley, can gauge the angle. Any off-angle measurement indicates put on 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 project a loud chirping or squealing appear. The cause tips to a glazed, put on or cracked belt. Dry or partially frozen tensioner pulley bearings can cause such noises by wearing out the belt prematurely.
Lever Arm Oscillation
A lever arm that repeatedly oscillates back and forth during idle or more speeds means the the within 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 sounds.