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What Are The Causes of Idler Pulley Noise?

An idler pulley or engine pulley steers and tensions the engine drive belt (serpentine belt), which drives several engine accessories including the power steering pump, alternator, AC compressor, and water pump. Any problem in the system will create idler pulley noise, indicating there is something wrong with the pulleys. A bad pulley may create plenty of troubles, affecting the serpentine belt and accessories connected to that belt.

How Many Idler Pulleys Does an Engine Use?

Most engines have just one idler pulley and one tensioner pulley. However, there could be more than one idler pulleys in some vehicles.

The idler pulley facilitates the motion of the engine belt, which means that it serves another smooth rotating point so the belt can loop around without any barrier. Thanks to this pulley, the belt can achieve the desired routing.

This idler pulley will eventually show signs of wear and become useless. Thee are some noises that will hint about the deterioration so that you can protect the serpentine belt and the engine by replacing it.

Reasons for Idler Pulley Noise

What are the causes that make idler pulley making these weird sounds? Detecting these noises at an early stage means that you can save several other accessories by taking the car to a mechanic.

For example, a mild squealing noise coming from the engine area indicates the beginning stages of the problem. This sound comes from the serpentine belt rubbing against the surface of the pulley. In severe cases, the pulley may slip off of its route or get stuck causing the belt to create loud squealing noise at the time of starting the engine.

idler pulley

Paying attention to idler pulley noise is important because the condition can turn from bad to worse in no time. Take the vehicle to an auto repair shop when the noise is lighter. Louder noise may indicate a severe problem that may take more money to get fixed.

Let’s see what could be the reasons for the pulley to make such unusual noises.

An Old or Worn-out Pulley

The pulley spins against the drive belt constantly unless the engine is off. Eventually, both the pulley and the belt start to wear off due to years of continuous spinning.

A worn-out pulley will have visible scuffs and other marks on its surface. A physical inspection will be enough to detect the scoring marks. The noises will be less noticeable at this stage. But their intensity will increase with time, and both components will lose tension at one point. When this happens, the belt is likely to slip from its route whenever you start the engine.

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Pulley Slippage

The initial squealing noises might become too loud when pulley wears out so much so that it starts slipping out of its slot. A displaced pulley means it can no longer help with steering the belt and maintains its tension. Also, this is likely to affect the components and belts connected to the drive belt.

The noise will keep increasing unless the worn-out pulley is replaced.

Severe Damage of the Pulley

This will happen if you keep ignoring the idler pulley noise coming from the engine area. In this extreme situation, the pulley will be so damaged that it will break completely. Of course, this does not happen in a minute or a day.

Deterioration of the pulley sets slowly by forming cracks on the surface. These cracks break the pulley apart a little bit at a time. Ultimately, the chain reaction of the damage and increasing wear due to continuous movement damages the serpentine belt too and breaks it completely sometimes.

idler pulley noise
The engine drive belt depends on the idler pulley.

A damaged serpentine belt can cause plenty of problems including a dysfunctioning power steering and air conditioning system. If the problem becomes severe, you will face issues like engine overheating and stalling.

Problems with the serpentine belt also create a squealing noise coming from the front side of the car but it will be louder and intense. You should never ignore engine belt issues as these could destroy the car’s engine.

The Costs of Replacing an Idler Pulley

An idler pulley replacement is not an expensive affair. A new pulley costs anywhere between $40 and $100, depending on the make and model of your car. The labor costs will be another $40 to $120. The auto repair shop may charge some extra fees and taxes. So, it’s possible to get the job done at around $200. you can cut the cost to half if you know how to do it and replace the pulley in your garage.

Whenever you hear idler pulley noise, take immediate action. As the drive belt is dependent on that pulley, ignoring the problem for long will lead to something serious.