What does the serpentine tensioner do?

The serpentine belt tensioner is a vital component of the accessory belt system. It maintains proper tension, so the belt remains tight around the pulleys it drives. The belt provides power from the crankshaft to engine accessories such as the power steering pump, the alternator, and the air conditioning compressor.  Proper tension is essential for efficient power transfer and to prevent the belt from slipping. The serpentine belt will naturally stretch over time and the tensioner can compensate for this by automatically adjusting tension to maintain optimal tightness.

Failure of the tensioner can result in the belt slipping or coming off entirely. This could lead to a loss of power to critical engine accessories. The result could be engine overheating, battery draining, and potential engine damage.

Signs of a failing serpentine tensioner

• A slipping belt can cause a high-pitched squealing noise. It will be most pronounced at start-up or during acceleration. This could be an indication that the tensioner is no longer adjusting properly.

• During a visual inspection of the serpentine belt, if the belt appears to be off-center or not running in a straight line, the belt could be under-tensioned. The extra slack in the belt allows the belt to move from side to side.

• If the battery light becomes illuminated on your dash it could be a problem with the belt, not the battery or alternator. A failed tensioner with a slipping belt may not provide the force needed to charge the battery. Likewise, if you experience problems with the AC or power steering system this could be due to an issue with the belt and tensioner.

• While the engine is off you can inspect the tensioner. If there is excessive movement or it feels loose it could be worn out.

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Causes of serpentine belt tensioner failure

Serpentine belt tensioners are built to withstand the demanding conditions of the engine bay, but they can still fail over time due to various factors.

• Wear and Tear: Like all mechanical components, serpentine belt tensioners are subject to wear and tear with regular use. Over time, the tensioner’s internal components such as the spring and pulley bearings can degrade, leading to decreased effectiveness and eventual failure.

• Bearing Failure: The pulley bearing within the tensioner can wear out or become damaged due to exposure to heat, friction, and contaminants like dirt and debris. A failing bearing may produce noise, vibration, or excessive play, affecting the tensioner’s ability to maintain proper belt tension.

• Tensioner Spring Weakness: The tensioner relies on a spring mechanism to apply tension to the serpentine belt. If the spring becomes weak or loses its elasticity over time, it may not provide sufficient tension, leading to belt slippage, noise, and accessory malfunctions.

• Excessive Belt Load: If the serpentine belt is subjected to excessive load or stress due to worn-out accessories, misaligned pulleys, or a damaged belt, it can place additional strain on the tensioner. This can accelerate wear and lead to premature failure of the tensioner components.

• Contamination and Corrosion: Exposure to moisture, oil leaks, road salt, and other contaminants can cause corrosion and rust to develop on the tensioner’s metal components, including the spring, pulley, and mounting bracket. Corrosion can weaken the tensioner’s structural integrity and hinder its operation.

• Incorrect Installation or Adjustment: Improper installation of the serpentine belt tensioner or incorrect adjustment of the tensioner’s position can lead to uneven belt tension, misalignment, and premature wear. It’s essential to follow manufacturer guidelines and use the correct tools and procedures when installing or servicing the tensioner.

One of the most common causes of wear and tear is a failed clutched alternator pulley. The clutch reduces the load and force transmitted through the belt and the tensioner. If you have experienced multiple tensioner failures it may be an indication that your clutched alternator pulley is no longer functioning properly. For more information on clutched pulleys, check out this blog article: Clutched Alternator Pulleys are Important.