5 Bad Serpentine Belt Tensioner Symptoms (Replacement Cost)

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One of the things that cause the serpentine belt to go bad is when the belt tensioner is bad or broken. The tensioner is one of the crucial components that help the serpentine belt to keep rotating and doing its function. As with other components, once the tensioner is about to fail, it shows different unusual signs.

So, what are bad serpentine belt tensioner symptoms? The signs of a failing belt tensioner are quite similar to that of a bad serpentine belt; you’d hear loud whining noise as you drive, and your engine may overheat more than it has ever done.

What Does Serpentine Belt Tensioner Do?

Put simply, the function of the tensioner is to retain a certain level of “tension” on the serpentine belt. This predetermined tension held by the tensioner is what keeps the serpentine belt running as designed, pulling all connected pulleys, and causing the car to cruise smoothly.

A bad tensioner would be tantamount to a bad serpentine belt, and if not treated urgently, the engine could get badly affected; if not wrecked/totaled. It is important you know the signs of a bad tensioner, and that’s what we’ve explained below.

Is It Safe To Drive With a Bad Belt Tensioner?

No, it is unsafe to drive with a faulty component; let alone, a component that has failed completely. Driving with a bad belt tensioner is very risky and poses greater damage to all the pulleys connected to the serpentine belt and even the engine too.

More so, a bad tensioner would cause a loud noise, which would definitely make driving uncomfortable. A bad tensioner can lead to serpentine belt failure, which in turn, causes overheating inside the engine, and that can cause more expensive damages.

Bad Serpentine Belt Tensioner Symptoms

1. Uneven/Unusual Belt Wear

When the tensioner is bad, the amount of tension it reserves for the serpentine belt won’t be up to the minimum, or it may exceed the maximum. Hence, it would cause the serpentine belt to wear out faster than it would have done due to age.

It is possible that a bad belt tensioner can cause the serpentine belt edges to fray, or in worse cases, break. So, when you start noticing uneven wear on your serpentine belt, one of the things to check is the tensioner.

2. Loud Unusual Squeaking and Whining Noise

 This is another common symptom of a bad serpentine belt tensioner. Because of the pressure exerted on the belt due to the bad tensioner, you will hear a loud squeaking noise when you first start the car.

The noise may continue if you start driving, and maybe louder when you try to accelerate or drive uphill.

3. Loose Serpentine Belt

Another important sign to note is a loose serpentine belt. Basically, the serpentine belt is designed to firmly hold all the pulleys connected to it; but when the tensioner is bad or broken, the belt may appear loose and won’t be able to drive those connected pulleys.

Thus, you will notice a drastic drop in the performance of your engine as it starts to lose power intermittently. A loose belt tensioner can cause a whirling sound when the car is idling, or even while driving.

4. Rust and Cracks

You may see cracks and rust on a failing tensioner. The rust typically bleeds between the arm and base of the tensioner.

However, sometimes, some of the damages caused by a failing tensioner cannot be seen until the tensioner is uninstalled. The best solution here is to replace the tensioner.

5. Failure of a Belt-Driven Component

The serpentine belt drives the alternator, AC compressor, water pump, and many others. A bad tensioner can cause one of these components driven by the serpentine belt to fail.

This happens because the tension retained by the tensioner is no longer enough to drive those components; hence, they start to crack or fail.

Serpentine Belt Tensioner Replacement Cost

Bad Serpentine Belt Tensioner Symptoms

You’d be lucky if you found out earlier that the tensioner is going bad. The average belt tensioner replacement cost is $150 – $350 depending on your car model, the level of damage, and the type of tensioner used. The labor cost for belt tensioner replacement is on average $80.

However, if the serpentine belt is already worn out, or one of the driven pulleys has been affected by the bad tensioner, you will need to replace the belt/component alongside the tensioner, and that could be quite expensive.

Frequently Asked Questions

What Does a Bad Tensioner Sound Like?

You’d hear squeaking, whirling, or rattling noise when the serpentine belt tensioner goes bad. This noise is caused due to lack of sufficient tension on the serpentine belt to drive the connected pulleys and keep the car cruising as expected.

Can I Drive Without Belt Tensioner?

It’s unlikely you would be able to drive without a belt tensioner. When the tensioner goes bad, it makes the belt itself wear out faster, and may also cause the belt to fall out and break. If the serpentine belt becomes affected, it is definitely impossible for your car to start and drive, or keep driving (if you were already driving).

Can a Bad Belt Tensioner Cause Vibration

Because a bad belt tensioner can cause damage to the connected pulleys, it is also possible to experience vibration when driving with a bad belt tensioner. But the most common scenario a bad tensioner causes is making the serpentine belt snap and break.

Will Bad Belt Tensioner Cause Overheating?

Definitely, it well. A bad belt tensioner can cause overheating because it would force the serpentine belt to stop driving the pulleys, which includes the AC compressor and water pump.


In conclusion, some of the most common bad serpentine belt tensioner symptoms include whirling noise, overheating, squeaking noise, and excessive wear on the belt itself.

It is important that you detect these symptoms earlier and replace the tensioner before it starts affecting other connected components, and the engine too. The cost of fixing or replacing a bad belt tensioner is below $400 (labor cost inclusive).

Read Also: Top 4 Symptoms of a Bad Timing Belt

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