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Serpentine Belt Noise – What Causes The Sounds?

Serpentine Belt Noise

The serpentine belt, also known as the drive belt, is the belt on a car engine that works in tandem with the car idler, tensioner, and idler pulleys inside of the accessory drive belt system helping to power the car. This serpentine belt provides the necessary power for the air conditioning, alternator, power steering, and the system water pump.

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If you open the hood in a modern car on the market with either a gasoline or diesel engine, you will notice at least one serpentine belt in your car. There can also be cars with two or three belts, while electric cars do not have any serpentine belts. The function of the serpentine belt is to drive accessories like the alternator, and differs from the timing belt. 


The timing belt runs the camshaft and is hidden under protective covers. So, what happens if the serpentine belt breaks or the serpentine belt noise is getting louder and louder during use? We will go through what causes the serpentine belt noise and the main symptoms and signs of a damaged serpentine belt. 

What is serpentine belt noise 


When your internal combustion engine is running in your car, this means that your serpentine belt is also running. This belt provides the much needed mechanical power to the steering pump, the air conditioning compressor, the alternator, and other accessories that power your car and keep it running smoothly. If you hear that there are noises coming from your engine area, then it might be due to the serpentine belt noise. 


No matter what issue your serpentine belt is facing or causing, colder temperatures can make them worse and cause a higher serpentine belt noise. As these problems get worse over time, the serpentine belt noise will get louder and more noticeable to the drivers and passengers. Of course, cold weather can cause squeaks to come from other parts of your car. If the serpentine btl noise is not directly occurring, then the noises may be caused by other accessories. 

Top cause of noisy serpentine belt


Along with common issues, cold weather is a catalyst to a loud serpentine belt noise. Along with other issues that can be exacerbated by cold weather, the serpentine belt can be directly affected. If your wheel well will build up ice over time, the strange noises will follow. If you hear squealing noises coming with your car, then it could be the engine or serpentine belt. 


In most cases in your vehicle, it will be that your serpentine belt is the culprit. These serpentine belt noises might get even louder and worse over time, or as you step on the gas pedal to accelerate. Here are just five of the most common reasons why your serpentine belt is making noise when the car is cold or while you are trying to go faster in your car or tow extra loads. 

Bad or worn tensioner


As you might have guessed, proper tension is key for any belt in your car. Usually, an old spring-loaded automatic belt can seize up or wear down over time, causing it to become weak. Without proper strength and tension, the serpentine belt will start slipping, causing it to wear faster and produce serpentine belt noise. 


Seized belt tensioners can cause a loose serpentine belt to completely fall off of the tensioner. The symptoms of a loose belt include serpentine belt noise when the engine is started or when you turn the steering wheel all the way to the left or the right. 


The serpentine belt is given the right amount of tension by the drive belt tensioner, which is basically a mechanism that is a pulley connected to the adjustable pivot. If you have a worn out or damaged tensioner in your car, then this will directly affect the tension of your serpentine belt that is dependent on the pulleys of the system. Your serpentine belt could come loose and cause serpentine belt noises, resulting in the louder sounds when you accelerate. 

Worn out belt 


Serpentine belts are supposed to have a lifespan or longevity of around 500,000 miles in older cars. However, the new serpentine belts are made from durable synthetic rubber that should be long lasting and durable in your vehicle. The name for this durable synthetic rubber is ethylene propylene diene terpolymer or EPDM, which can reduce the serpentine belt noises if the condition of the serpentine belt is intact. 


If your serpentine belt is made from this EPDM then it can last up to 100,000 miles. After that, you should notice the belt getting worn out and showing signs of replacement soon. This can cause the serpentine belt to move poorly over the pulleys and create serpentine belt noises. 

Belt misalignment


Sometimes, their serpentine belt might be in a good condition, but is misaligned meaning that the properties and materials are fine, but the serpentine belt has been misplaced. In this case, it could be due to the mechanic recently installing a new one in the car in the wrong space. If the recently installed serpentine belt is causing serpentine belt sounds, then they probably did not do a good job of aligning the belt onto the pulleys.


In addition, there could be issues with the hydraulic belt tensioner. Many cars have a hydraulic serpentine belt tensioner, where the spring of the belt is maintained by a shock absorber. Symptoms of a broken or damaged hydraulic belt tensioner include a leak from the tensioner or a rattling sound, causing the serpentine belt noise. 


The fix of this issue is that the belt tensioner needs to be replaced. The belt should also be replaced, unless it has just previously been replaced recently. A hydraulic belt tensioner replacement costs between $35 and $75, with the labor costing even more, between $75 and $150. 

Idler pulley misalignment


Your serpentine belt can become misaligned, but it is not the only part in your car that can be instead incorrectly. Aside from the pulley for the drive belt tensioner, the idler pulley can also be a catalyst to the serpentine belt noises due to the misalignment. The idler pulley is one of the pulleys that is supposed to keep the serpentine belt moving correctly and in-line. The function of the idler pulley is to help move the other engine accessories, and can cause serpentine belt noise if the pulley is misaligned. 


A serpentine belt is meant to run on various pulleys, like the idler pulley, and if any of the devices or tensioner pulley is not correctly aligned with the serpentine belt, the serpentine belt noise will occur, often in the form of a squeal. This problem is usually discovered after a new belt still squeals, wears down fast, or makes loud serpentine belt noise. A clear symptom that can alert you to this misalignment is increased wear on just one side of the belt. 


This can usually be seen visually during analysis of the belt. If you can see when the pulley is not lined up, the belt will squeak and the alternator can be loose and shifted under angle. This has caused the alternator pulley to be misaligned with the serpentine belt, so the belt squeals and wears down quicker. 


In addition to the idler pulley misaglinemtn, there can also be noisy idler pulley or tensioner bearing. To properly route and align the serpentine belt, many cars use pulleys, called the idler pulley, which spins on a bearing. When this bearing goes bad, it can produce a loud screeching sound and serpentine belt noise. 


Since several belt-driven devices can make a similar noise to this one when the bearing is damaged, this one might take a little bit longer to diagnose and be harder to find. Mechanics have to use special tools to look for the source of this noise, since a similar sound can be made from the power steering pump or alternator, instead of just the serpentine belt noise.


The repair of the idler pulley or tensioner bearing to remedy the serpentine belt noise requires a repair of the bearing coming in at between $15 and $35, plus $60-$170 in labor. 



If you do not take care of the issues that you notice with your belt and fix the serpentine belt noise, then the entire belt could eventually move off of the pulleys. This can cause the most noise with your serpentine belt, because all of your key engine parts and components will stop functioning altogether, creating a very bad situation that can further harm your engine. 

How to diagnose serpentine belt noise


Now that you know the signs and symptoms of the serpentine belt noise in your car, you need to figure out if this is the key issue, how to diagnose the problem, and where the serpentine belt noise is directly originating from. The squealing motor will get louder when you accelerate, and can be louder in cold weather. Fortunately, most belt noise can be relatively minor, but this does not mean that you can let it go and not fix the issue. 

Dry or cracked belt


Over time, the serpentine belt noise can come from a serpentine belt that has started to dry out due to old age, breaking down over time, damage, or the friction of being constantly in motion and the temperature coming from the engine itself. As this process goes on over time, the serpentine belt is no longer able to maintain the required tension to adequately grip the pulleys that link the belt together. 


When the pulleys begin to slip, the serpentine belt will slip as well, producing the serpentine belt noise. If you notice that your serpentine belt has any cracks when you are visually inspecting the component, there is a strong sign that it has been dried to the point where it is actually at the risk of breaking in two, meaning it is time to replace the belt and stop the serpentine belt noise. 

Coolant leaking 

Another main cause of the serpentine belt noise is prolonged exposure to coolant in the system. If you have recently added antifreeze to your radiator to keep your car cool and regulate the temperature, some of the coolant might have spilled onto your serpentine belt. This can quickly cause the serpentine belt noise and squealing sound. 


The same is true if any component of your cooling system is leaking fluid, as the engine fan can blow very small amounts of coolant back onto the serpentine belt, causing antifreeze to congeal on the belt. Unforatuenly, it is not easy and quick to clean antifreeze from the rubber serpentine belt once it has sunk in. This means that the main fix of this issue is to get a serpentine belt replacement to remedy the serpentine belt noise. 

Idler pulley loose 


A loose serpentine belt that is slipping will squeal and produce audible serpentine belt noise. If your belt is in good shape and you do not believe it is cracked or damaged and is not dried out over time, then it could be a good idea to check the tension on the idler pulley to make sure it is able to perform the ecorect function of taking the slack out of the serpentine belt as the pulley spins. 

When to replace serpentine belt


The serpentine belt is supposed to last from around 30,000-100,000 miles, but can sometimes undergo damage that makes the longevity a bit shorter. Most car manufacturers do not specify the exact intervals of serpentine belt replacement, but instead recommends inspecting the serpentine belt during regular services. For example, certain car manufacturers recommend the serpentine belt to be replaced at specific times. 


When you take your car to get a regular oil change service to keep the levels topped up, a mechanic will look for any signs of damage, like cracks, splits, damaged edges, missing chunks, glazing, or other signs of wear. In most cases, it is easy to see when the belt is worn out by visual signs of damage and cracks. A worn-out serpentine belt must be replaced in order to keep the car running smoothly, or if you find the serpentine belt to be soaked in oil, stretched, or the belt making noise.


The replacement cost of the serpentine belt will usually cover two serpentine belts, since you should replace both at the same time to save on labor. It is also a good idea to replace the old serpentine belt if you are planning on going on a long road trip and putting lots of miles on the car. Replacing a serpentine belt costs between $18 adn $75, plus between $50 and $150 for labor. 

Can I replace the serpentine belt DIY?


Although the serpentine belt could be pretty easy to replace in some cars if the serpentine belt noise is bothering you, it can also be pretty difficult if you are not used to doing any auto work. To replace the serpentine belt, you will need a diagram to show the proper routing. For some cars, the routing can be depicted in the owner’s manual to give you an idea of what you need to do in the vehicle. 


In some front wheel drive cars with a mounted engine transversely. The space between the engine and the frame can be quite small and make the serpentine belt replacement kind of difficult and harder to do than other repairs. In some cars, a special tool can be needed to release the belt tensioner. 

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