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How To Diagnose Serpentine Belt Noise + 8 Causes & Solutions

October 16, 2021

Is your serpentine belt making a squealing noise? 

What should you do?
And why is the serpentine belt making a noise in the first place?

In this article, we’ll learn how to identify serpentine belt noise, what causes it, and what to do about it.

This Article Contains:

(Click on the links below to jump to a specific section)

Let’s start.

How To Identify Serpentine Belt Noise

There can be quite a few reasons why you hear a squealing noise when you drive.
To easily identify a serpentine belt noise, keep an eye out for these signs:

Note: A bad serpentine belt alone won’t set off any dashboard lights, so it’s important to be alert for any failings in your car’s system. 

If you detect something, get it checked immediately as the serpentine belt directly influences vital engine components like your alternator and power steering. 

Serpentine Belt Noise: 8 Common Causes

If you keep hearing that high pitch squealing whenever you start up your engine, there can be different causes for it.

Here are some of them:

1. Worn Belt Or Dry Serpentine Belt

With time a serpentine drive belt will go bad, like most car parts. The good news is new car models come with durable belts (engine belt, alternator belt, timing belt, etc.) that last longer.

However, you should get your old belt replaced with a new belt after around 75,000 miles
If you don’t, you’ll have a broken serpentine or fan belt in the most unpredictable moments.

A serpentine belt noise can also come from a fan belt that has started to dry out. 
That squealing sound can arise due to the constant friction due to motion. The temperature coming from the engine can also make a belt dry. 

All these reasons result in a weaker serpentine belt that can no longer maintain the required tension needed to grip each tensioner pulley properly, linking the belt together. 

Additionally, if any pulley begins to slip, the serpentine belt will slip too, producing that annoying squealing sound.

It’s also a good idea to pop the hood and visually inspect your old belt for cracks. 
If there are any cracks, you have a dried belt that can snap anytime.

In this instance, the only way to stop the serpentine belt noise is by getting a replacement belt installed by a mechanic.

2. Worn Out Pulley Or Wrong Pulley Alignment

Did you know it’s not just the serpentine belt (alternator belt) that causes the squeal or other noises?

The whole thing is made up of a pulley system with spinning pulley grooves that hold the belt in place as it whips around.

If any tensioner pulley begins to wear out with time, it’ll create more of a chirping noise. You’ll also hear the chirping noise if the pulley grooves are damaged. 

This happens over the years due to friction, leading to cracks in the belt. If these cracks increase in number, the belt tension and the tightness in the pulley system will reduce, resulting in slippage or snapping.

Fortunately, professional mechanics can fix any misaligned pulley or replace any tensioner pulley easily. 

3. Exposure to Coolant

Antifreeze (engine coolant) is a colored liquid that’s mixed with water to help regulate your engine through extreme temperatures.

As the temperature changes from hot to cold outside, your car will pump the coolant throughout the engine block to provide an even operating temperature. 

But this temperature regulator can be dangerous too. 
Even the tiniest bit of coolant fluid can damage a serpentine belt or drive belt. It usually drips from a leak in the coolant hoses or is blown out from the engine fan and causes a belt squeal.

Unfortunately, you can’t wash off the antifreeze once it has sunk in on the belt, and it damages the belt immediately. Even though you come across some belt dressing products that claim to reduce the squealing or squeaking noise, you’ll mostly need a replacement belt to fix the belt noises.

4. Cold Weather

The weather can also affect how long a serpentine belt will last.
Cold temperatures can make the belt material brittle and prone to faster damage. 

Here’s the good news: If you notice the squealing noise is powerful in the morning when it’s cold, but reduces as the engine warms up and the day gets hotter, then you probably don’t have a bad belt.

However, get it checked out by a mechanic to confirm the cause for the squeaky belt and find out if you’ll need a serpentine belt replacement to eliminate that belt squeal. 

5. Misaligned Belt Due To Improper Installation

A serpentine belt replacement might be the easiest thing a mechanic may do for you. 
However, due to the high-tension nature of the drive belt, it needs precision on the track to function properly.

If the replacement belt isn’t installed properly, even a brand new belt and new belt pulley won’t stop the squealing noise.

Fortunately, it’s quite easy to detect this issue. 
If you’ve just got a new serpentine belt installed and yet you hear the squealing noise, chances are your mechanic didn’t do a good enough job. 

Let your mechanic check the belt and determine if there’s a misaligned pulley or belt tensioner. Any element of the belt design that isn’t installed right can disturb the whole system causing the squeal.

6. The Idler Pulley

If your belt looks fine and isn’t dry, there can be an issue with the idler pulley. 

What’s an idler pulley?
The idler pulley is one particular pulley in a set driving the belt system of a car.

This pulley regulates the belts connected to the crankshaft and helps move numerous engine accessories. Some of the accessories include the alternator, power steering pump, and AC compressor.

The idler pulley has to be strong enough to hold the serpentine belt in place with the right tension as it spins. If it doesn’t, the belt may slip, and the annoying squeal will start.

Call a mechanic to check the tension on the idler pulley. 
If it’s loose, then they’ll tighten your idler pulley.

It’s also a great opportunity for them to identify a worn bearing inside the idler pulley that may be adding to the belt squeal.

7. Bad Tensioner

The belt tensioner provides the correct amount of belt tension, allowing the serpentine belt to operate optimally. It’s basically a mechanism where a pulley is connected to an adjustable pivot. 

Clearly, proper tension is necessary. 
Without it or with seized belt tensioners, a serpentine drive belt will start to slip, damaging it faster. And as a result, it’ll produce the belt noise. 

Normally, an old or bad spring-loaded automatic belt tensioner can become weak. Such a belt tensioner can make a loose serpentine belt fall off the tensioner.

How can you tell if you have a loose serpentine belt or tensioner?
You’ll hear the belt noise when you shift the power steering wheel all the way to the left or the right, or when you accelerate.

If your vehicle utilizes a hydraulic belt tensioner (a belt tensioner where a shock absorber supports the spring of the belt), issues can manifest in other ways.

How to tell if you have a broken or damaged hydraulic belt tensioner?
You may spot a tensioner leak or hear a rattling noise, producing the serpentine belt noise.

8. Belt Slippage

Slippage can be due to loss of belt tension, a weak automatic tensioner, or wrong pulley alignment.

When the belt slips, the friction between the belt and accessory drive pulleys causes the drive belt to overheat, producing a high-pitched squealing noise.

The bottom line is, if you spot issues with your serpentine drive belt, get it checked out by a professional mechanic ASAP.

If you ignore the belt noise, the entire belt could eventually slide off of the pulleys. And all the key engine components will stop functioning. Don’t take this lightly because a squeaky belt can also harm your engine.

So what can you do?

What Can I Do If I Hear A Serpentine Belt Noise?

A damaged or failing serpentine belt that makes a squealing noise and is usually a serious matter. 

Contacting a mobile mechanic and repair service like RepairSmith is a great idea. It’s a convenient auto repair solution that’ll bring you the best quality serpentine replacement belt and install it.

With RepairSmith, you get:

Wondering about the price estimate?
Find out how much a RepairSmith serpentine belt replacement costs here.

Final Thoughts

The serpentine belt (also known as a fan belt, alternator belt, or drive belt) is a critical car component.

Hearing a sharp squeaking noise or a loud grinding noise are tell-tale signs of wear. 
It’s your car telling you something’s not right, and it may be your car’s broken or old belt.

Get it replaced with a new belt as soon as possible because the process is relatively inexpensive and quick. 

To make things easier, just reach out to a professional like RepairSmith. It’s a mobile mechanic and auto repair shop that comes to your doorstep (or anywhere you are) for your serpentine belt replacement!