What does the strain pulley do?
A drive belt tensioner is a pulley mounted on a spring system or adjustable pivot point that is used to keep tension on the engine belts. … Both are used to keeptension on the engine serpentine belts to ensure that they can travel the many engine accessories.
How do you adjust a tensioner pulley?
Turn 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 I 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 can cause power loss and damage to your belt-driven devices. You might 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 warmth. Pulleys are usually made of either plastic or metallic, so check the pulley itself for any damage as well. At O’Reilly Automobile Parts, we have tensioner pulleys available for many vehicle models.
The computerized 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, so that the other equipment pulleys rotate at the same rpm (revolutions per minute) while beneath the same secure pressure. Tensioner pulleys can also absorb mild shock loads that happen when the air conditioning unit cuts on and off. As a continuously 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 end of the engine. Put through puddled water “splash-up,” as time passes the tensioner arm and pulley device can rust. Rust can freeze the programmed tensioner device or rot the shaft bearings, that will cause a frozen position in the adjustment pressure. Without the correct pressure, 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 permit the serpentine belt to slip on the tensioner pulley and burn up. Overheated pulley temp 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 weak spring display as glazing on the underside of the serpentine belt, with an occasional flickering of the dashboard’s charging light 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. Terrible bearings cause an audible growling sound. The external ends of the serpentine belt will fray and stretch out the belt. Ultimately the rubber belt grooves flatten out and cause important slippage. An excessively wobbling pulley can toss the belt off, triggering all the extras to quit functioning.
Lever Arm Freeplay
Some tensioner pulleys have 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 one 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 then flushing it against another item pulley, can measure the angle. Any off-position measurement indicates donned shaft bearings in the pulley casing.
Serpentine Belt Noise
A moderately worn serpentine belt produces a constant squeaking noises during engine idle. Belts that contain worn severely job a loud chirping or squealing audio. The cause factors to a glazed, donned or cracked belt. Dried out or partially frozen tensioner pulley bearings could cause such sounds 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 can manifest itself with intermittent chirping sounds.