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What Is an Idler Pulley?

What Is an Idler Pulley?

Do you know what is the ‘brain’ of your car? Yes, it is your engine. A powerful engine is important for the smooth running of a car. On the engine, there are drive belts that make sure the flawless working of different components of a car.

These drive belts are connected to various components such as the power steering pump, the water pump, the air conditioning compressor, and the alternator. They depend on the power produced by the engine.

A car’s engine, however, produces energy from the movement of its pistons. The energy generated has to be converted into rotary motion. The idler pulley is used to apply force in a linear and rotational motion. This way, the proper functioning of a vehicle’s belt system is largely depended on an idler pulley.

What Is the Idler Pulley?

We now know that the engine needs supportive devices that can convert the energy produced by it into other forms so that it can be transmitted to different components required for the running of the vehicle. Among such components is the idler pulley. Let’s have a look at how it operates.

Function of the Idler Pulley:

The idler pulley drivers the belt system of a vehicle which is connected to the crankshaft. It produces movement in various components of engine such as the alternator, the AC compressor, etc.  

Design of the Idler Pulley:

The idler pulley is made up of a sheave or a wheel with a groove that runs along its end. It holds a belt that sits in the groove and runs over the roller. The wheel is rotated by the power generated by the crankshaft

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A Bad Idler Pulley

The idler pulley is inherently prone to wear and tear and damages. You may also face an idler pulley problem. But how would find out? Here are some signs that can tell you that your idler pulley has really gone bad.


While driving your car, have you ever noticed that your car is squealing – making a high-pitched sound? This squealing is the first indicator that suggests that the bearing of your idler pulley has gone bad. The squealing also indicates that the surface of the pulley is no longer smooth and has worn out. Don’t neglect the sound of squealing and get your car checked in a timely manner.

Visible Wear

There are a considerable number of people who physically check their car before they go on a ride. For such people and abnormalities are visible instantly. Such people can see any scuff marks on the pulley or other related things that may indicate that the pulley has completed its useful life.

Belt Travel

A pulley is responsible for the smooth working of the vehicle’s belt system. So, if you see that the engine belt is wobbling or moving from side to side, you must know that your idler pulley needs replacement.

The Final Word

An idler pulley ensures that you have a comfortable ride. Watch out for the signs that tell your pulley is not working smoothly so that you can get the problem fixed as early as possible.