Serpentine Belt Tensioner

From our article on serpentine belts:

The serpentine belt runs across the front of most engines, providing power from the crankshaft to each of the engine's accessories (alternator, power steering pump, air conditioning pump, etc). Sometimes it is a single belt, often it is two or even three.

On single-belt systems, the long and complex belt path is often held in place and at the proper tension by a serpentine belt tensioner. These are small pulleys that use a spring or gearing system to keep proper tension on the belt without adding undue friction.

Tensioners are usually located near the center of the belt's travel - usually on the left- or right-hand side of the engine when looking at it head-on. In rare applications, it may be at the top-center.

The tensioner is also usually the point at which a mechanic will loosen the serpentine belt in order to remove and replace it. Most tensioners have a release bolt that can be loosened or removed to allow the tensioner to slack and disengage the belt, making it loose and easy to unwind from the pulleys.

If anything is wrong with the serpentine belt tensioner, the belt will begin to squeal or will fail. This is common in older tensioners whose springs have lose their full strength. Because the tensioner is usually relatively easy to get to, replacement costs are minimal (total will depend on the engine, usually $100 parts + labor).

The tensioner is one of the most important parts of the engine's operation as it keeps the serpentine belt properly turning to keep accessories like power steering, the alternator (providing electrical power), and the engine fan operating.

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