Most vehicles on the road today have an idler pulley. The idler pulley is a main component of every vehicles “belt loop”. This pulley assists the regulation of how belts run from the crankshaft to transfer motion to other main car parts and engine accessories to supply them with power. The idler pulley consists of a set of pulleys on which, in modern vehicles, the serpentine belt is routed over in order to power necessary engine components and accessories including the alternator, power steering pump, air conditioning compressor, water pump, A/C compressor and sometimes other components. Car makers almost always provide belt diagrams that show the belt and pulley route. These diagrams are usually found on a sticker under the hood and in the vehicles owner manual, but if not, you can probably find your vehicles belt diagram on our website.
Idler pulleys, in general, make it possible to replace serpentine belts on serpentine belt equipped vehicles. The pulley is usually adjustable and often times paired with a belt tensioner. These tensioners can be spring loaded, hydraulic, or completely manual depending on the automobile manufacturer. The tensioners aren’t only used as a tool to replace belts; they also provide a way to apply different levels of tension to serpentine belts. Tensioners are adjusted usually by the turn of a screw. Depending on which way the screw is turned, the amount of tension is increased or decreased. Having the correct amount of tension on a belt is essential to the life of the serpentine belt and all the pulleys it runs through.
Due to the things some manufacturers use to make idler pulleys, they sometimes have a tendency to degrade over time because of the stress placed on them by the serpentine belt which is constantly putting friction on the pulley. Pulleys should last much longer than the belts they guide, but they should be checked from time to time for signs of abnormal wear. When checking a vehicles serpentine belt, a vehicle owner can easily determine if the pulleys are going bad. If one goes out, it will be immediately obvious because the belt will show extremely obvious symptoms and the vehicle will become un-drivable.