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?
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 eliminate. Tighten the tensioner pulley by turning the adjustment bolt clockwise with the ratchet and socket before belt is tight.
How do I know
A tensioner pulley courses 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 devices. You may have a failing tensioner pulley in the event that you hear any squeaking or squealing beneath the hood. Bearings on the pulley can wear out, causing noise and heating. Pulleys are usually made of either plastic or metallic, so check the pulley itself for just about any damage aswell. At O'Reilly Vehicle 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 constant tension. Its design allows 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 safe pressure. Tensioner pulleys can also absorb gentle shock loads that happen when the air conditioner cuts on and off. As a continuously rotating aspect, 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 of the engine. Put through puddled water "splash-up," as time passes the tensioner arm and pulley device can rust. Corrosion can freeze the computerized tensioner device or rot the shaft bearings, that will cause a frozen job in the adjustment pressure. Without the proper stress, the belt can slide.
Debris Contamination
Rocks, gravel and other road debris could be thrown up in to the tensioner pulley grooves and jam the device. This can allow the serpentine belt to slide on the tensioner pulley and burn up. Overheated pulley heat 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 triggers the belt to flutter and skip instead of maintaining a constant pressure on the pulley. Symptoms of a fragile spring present as glazing on the lower of the serpentine belt, with an intermittent flickering of the dashboard's charging light indicator. Squealing or squeaking will become read at the belt location.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, this means the interior shaft bearings have worn. This may cause a pulley misalignment. Undesirable bearings cause an audible growling noises. The external ends of the serpentine belt will fray and stretch out the belt. Eventually the rubber belt grooves flatten out and trigger 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 maximum range that the pulley can travel. If the lever arm of the tensioner rides under or over 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 up 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 measure the angle. Any off-position measurement indicates worn shaft bearings in the pulley housing.
Serpentine Belt Noise
A moderately worn serpentine belt gives off a constant squeaking noise during engine idle. Belts that contain worn severely job a loud chirping or squealing sound. The cause items to a glazed, worn or cracked belt. Dried out 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 inside damper mechanism in the tensioner pulley has weakened or broken. This triggers sporadic tension pressure on the belt and will manifest itself with intermittent chirping noises.