Symptoms of a Bad or Failing Belt Tensioner | Autance

The modern internal combustion engine comes with different components that allow it to convey power to the wheels and to…

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Symptoms of a Bad or Failing Belt Tensioner | Autance © Symptoms of a Bad or Failing Belt Tensioner | Autance

The modern internal combustion engine comes with different components that allow it to convey power to the wheels and to accessories in your car. One of these components is the belt tensioner. Like all automotive parts, it has a lifespan. Unusual wear can reduce the service life of such a device, requiring replacement sooner than expected. It is important to recognize the various symptoms of a failing or a bad belt tensioner. This will help you determine the precise action to take.

The Belt Tensioner

Before we start looking at the symptoms of a failing belt tensioner, let us first get to know this component.

The belt tensioner is an important part of the drive belt system in your car. This system is responsible for converting some of the power generated by the engine. This power drives the alternator, water pump, power steering pump, and air conditioning compressor, among others. It is the responsibility of the belt tensioner to ensure that the drive belt has the right amount of tension to power the different accessories.

A belt tensioner is like a pulley that is mounted on an adjustable pivot point or a spring mechanism. Both mounts allow for the more efficient application of tension on the belts. Pivot designs allow for manual adjustments in the tension. Spring tensioners operate automatically. This means it adjusts the tension on the drive belts without external manipulation.

The belt tensioner in your car consists of four principal parts. These include the pulley, the tensioner arm, the spring, and the base. The pulley is what allows the movement of the drive belt. The spring keeps the drive belt in its correct tension. The tensioner arm is a mechanism that allows for the adjustment or the removal of the drive belt. It delivers enough slack on the drive belt for easier adjustments. The base is what holds all the different parts together.

Symptoms of a Failing Belt Tensioner

We now know that the belt tensioner is what maintains the correct tension on the drive belt system. If we are not able to maintain correct tension, then it will be difficult to run the different components that rely on the drive belt system. Some of the more common symptoms of a failing or bad belt tensioner include the following.

Squeaking or Grinding Noise

One of the most common symptoms of a failing belt tensioner is unusual noise coming from either the tensioner or the drive belts. If the drive belt noise resembles a squeal or a squeak, it is possible that the belt tensioner is loose. This is especially the case when starting the engine first thing in the morning. Since the tensioner is not able to maintain the correct tension on the belts, it produces a squealing or squeaking sound. This is most evident on the drive belts.

If the noise you hear is similar to a grinding sound, then it is possible that the tensioner bearings or the tensioner pulley is the problem. These parts tend to wear out. This is what causes the grinding noise since the metal parts will be rubbing against each other.

Unusual Belt Wear

This is another symptom of a failing belt tensioner. Depending on the type of drive belt that you have in your car, then you should see even patterns throughout the length of the belt. Over time, these belts tend to wear out. There are also instances when the drive belts wear out sooner than one can expect. This can be due different causes.

One of the more important reasons of unusual belt wear is a problem in the pulley of the drive belt tensioner. If the pulley is problematic, it can lead to the fraying of the drive belt’s edges. In more severe instances, a bad tensioner pulley can cause the drive belt to break.

Failure of the Belt-driven Accessories to Operate

Since the belt tensioner keeps the proper spinning of the drive belts in the car’s engine, certain components or accessories may fail to operate if there’s a problem with the tensioner. For instance, the alternator may not work. If this happens, then you will not be able to power up your car’s electrical components. You will also not be able to charge your car’s battery while driving.

A failing belt tensioner can also cause problems in the water pump. This is a very important component of the engine as it circulates engine coolant through a closed system of tubes, hoses, and other components. If it fails to operate properly, then you can have issues with engine overheating. As a consequence, this can damage your car’s engine.

The air conditioning compressor may also fail to work if there is an issue with the belt tensioner. If this happens, then you will be driving without your air conditioning. It should be okay if you are cruising. It may be a different story if ever you find yourself in the middle of a traffic jam. The heat will be unbearable for everyone in your car.

There are different reasons why these belt-driven accessories fail, of course. Since they get their power from the engine via the drive belts, it is always safe to assume that the belt tensioner is also problematic.

In many cases, the belt tensioner requires replacement. If not, then it will not be able to maintain the correct tension of the drive belts. This will lead to a reduction in power transmission to the accessories.

Bleeding Rust and Presence of Cracks

If you notice rust forming or bleeding between the belt tensioner arm and base, it is a sign that the tensioner needs prompt replacement. This often arises because of excessive wear in the internal components of the tensioner. It is also possible that you will see cracks on the tensioner itself. Your mechanic may also notice damage to the housing and bracket of the belt tensioner. The most common areas where cracks or damage can occur include the mounting bolts and the tensioner stops.

The sad thing about these is that you will not see these problems unless you remove the tensioner itself. For obvious reasons, only a mechanic has the right competencies to perform the job.

Excessive Wear of Pulley Bearing

If you’re able to remove the drive belt you can try to rotate the pulley. If you notice that there is resistance, roughness, or noise every time you turn the pulley, then there’s a chance that the problem is in the pulley bearings.

You might think of replacing only the pulley bearings in this case. Mechanics will tell you to replace the entire belt tensioner system. This is to help avoid compromising the state of the tensioner. There is no way of knowing whether the tensioner is also affected by the pulley bearing wear. It is best to replace the entire assembly to be safe.

Visible Signs of Pulley Wear

Looking at your tensioner pulley, it should be free from cracks, dents, and chips. The surface should also be smooth. The grooved surfaces should not have debris or any other particle within the grooves. The groove’s high points should also be equal in height. One major cause of pulley wear is the wearing of drive belt into the pulley.

The entire belt tensioner assembly needs replacement. Don’t think that only the pulley needs replacement. It has to be everything to maintain the integrity of the system.

Excessive Sideward Movement of the Tensioner Arm

Turn on your car’s engine and watch the tensioner arm. It should stay in a tight position. If the tensioner arms make large swings, it is possible that there is an issue with the spring torque or the damping system. It is also possible that there’s a problem with the overrunning alternator pulley or the torsional vibration damper.

Identifying the issues in these components needs the expertise of a mechanic. As for the excessive oscillations of the tensioner arm, you can make accurate observations that you can share with your mechanic.

Loss of Tensioner Spring Force

Use a wrench to move the belt tensioner arm through its range of motion. What you want to see is that there is resistance to the movement that you apply. If you notice that there is no resistance at all, then the problem is in the tensioner spring. In such cases, mechanics will say that the spring no longer has the force to resist tensioner arm movements.

The loss of tensioner spring force can also come with squealing noise from the drive belt. This occurs because of belt slippage. It is also possible that a belt-driven component will no longer rotate.

The belt tensioner in your car is an important component. It maintains the correct tension on the drive belts. This helps facilitate the transmission of power to the different accessories of your car. Because the belt tensioner is an integral component of the engine, only a professional mechanic with many years of experience can handle these issues.


  1. Tensioner – Wikipedia
  2. How to Tighten a Drive Belt – wikiHow
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