What does the tension pulley do?
A drive belt tensioner is a pulley mounted on a spring device 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 so that they can drive the many engine accessories.

How do you adapt a tensioner pulley?
Change the adjustment bolt privately, top or bottom 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 before belt is tight.
How do you know

A tensioner pulley manuals the belt around the tensioner and allows the belt to spin as the tensioner maintains pressure against it. A failing tensioner pulley can cause power loss and damage to your belt-driven devices. You may have a failing tensioner pulley if you hear any squeaking or squealing under the hood. Bearings on the pulley can wear out, causing noise and temperature. Pulleys are usually made of either plastic or steel, so check the pulley itself for any damage aswell. At O’Reilly Car Parts, we have tensioner pulleys designed for many vehicle models.

The automated pulley tensioner has an internal spring-loaded mechanism that keeps the serpentine belt under regular tension. Its design permits it to keep the serpentine belt taut, to ensure that the other accessory pulleys rotate at the same rpm (revolutions per minute) while beneath the same safe pressure. Tensioner pulleys may also absorb slight shock loads that happen when the air conditioning unit cuts on / off. As a constantly rotating element, the pulley tensioner can provide 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 mechanism can rust. Corrosion can freeze the automatic tensioner device or rot the shaft bearings, that will cause a frozen position in the adjustment pressure. Without the proper pressure, the belt can slip.
Debris Contamination
Rocks, gravel and other highway debris can be thrown up into the tensioner pulley grooves and jam the system. This can permit the serpentine belt to slide on the tensioner pulley and lose. Overheated pulley heat range results, and eventually the serpentine belt will melt and snap off.
Pulley Tensioner Spring
The pulley tensioner spring inside 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 strain 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 light indicator. Squealing or squeaking will become observed at the belt position.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, this means the inside shaft bearings have worn. This may cause a pulley misalignment. Poor bearings cause an audible growling sound. The outer ends of the serpentine belt will fray and stretch out the belt. Gradually the rubber belt grooves flatten out and trigger key slippage. An excessively wobbling pulley can throw the belt off, triggering all the equipment to quit functioning.
Lever Arm Freeplay
Some tensioner pulleys possess markings on the housing that indicate the maximum selection 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 which has jammed in one position.
Pulley Misaligment
The tensioner pulley face must match to the other accessory pulleys with a parallel alignment. Placing a long, straightedge ruler against the facial skin of the tensioner pulley, and then flushing it against another item pulley, can measure the angle. Any off-position measurement indicates worn shaft bearings in the pulley casing.
Serpentine Belt Noise
A moderately worn serpentine belt produces a constant squeaking noise during engine idle. Belts that have worn severely project a loud chirping or squealing audio. The cause things to a glazed, donned or cracked belt. Dry or partially frozen tensioner pulley bearings can cause such noises by deteriorating the belt prematurely.
Lever Arm Oscillation
A lever arm that repeatedly oscillates backwards and forwards during idle or higher 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 sounds.