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

How do you adjust a tensioner pulley?
Turn the adjustment bolt privately, top or bottom of the pulley counterclockwise with the ratchet and socket until the accessory 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 I 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 could cause power damage and harm to your belt-driven devices. You could 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 heating. Pulleys are usually manufactured from either plastic or metal, so check the pulley itself for just about any damage as well. At O’Reilly Automobile Parts, we’ve tensioner pulleys designed for many vehicle models.

The programmed pulley tensioner comes with an internal spring-loaded mechanism that keeps the serpentine belt under constant tension. Its design enables it to keep carefully the serpentine belt taut, in order 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 moderate shock loads that happen when the air conditioner cuts on / off. As a continuously rotating component, the pulley tensioner can give off some warning signs 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 mechanism can rust. Corrosion can freeze the computerized tensioner device or rot the shaft bearings, which will cause a frozen placement in the adjustment pressure. Without the proper tension, the belt can slide.
Debris Contamination
Rocks, gravel and other highway debris could be thrown up into the tensioner pulley grooves and jam the mechanism. This can allow the serpentine belt to slide on the tensioner pulley and burn. Overheated pulley temperature results, and eventually 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 exposure to heat. This causes the belt to flutter and skip rather than maintaining a constant pressure on the pulley. Symptoms of a fragile spring demonstrate as glazing on the underside of the serpentine belt, with an intermittent flickering of the dashboard’s charging light indicator. Squealing or squeaking will always be heard at the belt position.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, it means the interior shaft bearings have worn. This will cause a pulley misalignment. Awful bearings cause an audible growling noises. The outer ends of the serpentine belt will fray and stretch out the belt. Sooner or later the rubberized belt grooves flatten out and trigger major 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 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 to the other accessory pulleys with a parallel alignment. Placing an extended, straightedge ruler against the face of the tensioner pulley, and flushing it against another item pulley, can measure the angle. Any off-position measurement indicates worn shaft bearings in the pulley housing.
Serpentine Belt Noise
A moderately put on serpentine belt produces a constant squeaking noise during engine idle. Belts that have worn severely task a loud chirping or squealing audio. The cause items to a glazed, put on or cracked belt. Dried out or partially frozen tensioner pulley bearings can cause such noises by deteriorating the belt prematurely.
Lever Arm Oscillation
A lever arm that repeatedly oscillates back and forth during idle or higher speeds means the the within damper mechanism in the tensioner pulley has weakened or broken. This causes sporadic tension strain on the belt and can manifest itself with intermittent chirping sounds.