Is It Safe To Drive With a Bad Belt Tensioner?

A serpentine belt tensioner is something that applies a regulated amount of pressure to the serpentine belt so it can spin the alternator pulley, AC compressor pulley, power steering pump pulley, and other as needed.

”It is not safe to drive with a bad belt tensioner because the belt tensioner ensures sufficient tension to power the accessories. As the tensioner wears, the belt can slip at the accessories creating noise, excessive heat at the accessory pulleys, and reduce accessory performance. Overtime, this can cause permanent damage to the accessories.”


Is It Safe To Drive With a Bad Belt Tensioner?

When it comes to preventing premature wearing or permanent damage to the accessory pulleys, it is definitely not safe to drive with a bad belt tensioner.

A bad or worn belt tensioner can no longer perform its key mission which is to provide enough tension so the belt can spin the alternator pulley, ac compressor pulley, power steering pump pulley, and other pulleys.

Once the belt tensioner gets worn, the belt can start slipping, create noise, excessive heat and reduce the accessory performance. This means that your alternator will no longer be able to work in full capacity and recharge your battery. The ac compressor efficiency will dramatically reduce, as well as your power steeringOpens in a new tab.

Belt Tensioner Modes Of Failure

Is It Safe To Drive With a Bad Belt Tensioner

The belt tension is the key to the proper functioning of the accessory belt drive system. Transferring torque to run the accessories is the main task of the belt tensioner and anything that interferes with that transfer is a problem.

In the past, much of the focus of torque transfer failure has been on the belt itself, when in fact, belt tension is the culprit. Here are the 5 most common belt tensioner modes of failure:

1. Belt Slip

If your belt tensioner is worn, it can cause the belt to slip at the accessories and create squealing noise, excessive heat at the accessory pulleys, and to reduce the accessory performance. This can result in permanent damage to the belt and the accessories.

2. Belt Misalignment

As the belt runs through the accessory belt drive system, all of the pulleys should be in alignment. A tensioner will cycle a billion times over a hundred thousand miles causing the tensioner pivot bushing to wear. When the pivot bushing wears, the tensioner arm can move out of alignment. This causes the belt to run uphill on the pulley damaging the belt and causing a lot of noise. The system can only tolerate one degree of misalignment. For each degree over that, thirty degrees of heat is generated for the belt and accessory bearings, leading to accessory failure.

3. Failure of the Tension Damper

The damping mechanism is critical to controlling vibration and power fluctuations. When the damper is worn, it can no longer limit the tension or arm movement which results in the belt slapping against the next accessory. Eventually, the accessory will fail prematurely.

4. Belt Wear/Mating

It makes sense that the belt and pulley must mate properly in order to provide the necessary friction to assure proper accessory function. With modern EPDM belts, it’s hard to visually determine when the belt is worn to the point it will affect belt pulley mating.

A new belt mates tightly with the pulleys creating a belt pulley interface providing necessary traction while leaving a channel to evacuate water and other debris. The belt loses material with normal wear.

With just 5% belt wear, the belt will not mate properly with the pulley losing traction in the ridges. The belt just rides overt he pulley wandering and slipping over the top instead of transferring power.

The evacuation channel gets larger as the belt wears allowing water to get between the pulley and the belt pushing up on the belt causing it to hydroplane on the pulley.

5. Belt Slip on Alternator

Each accessory powered by the ABDS has its own job to do and relies on a smooth and steady source of drive power. When the ABD system is workingOpens in a new tab.

The alternator, as an example, will be spinning at the design speed creating electricity to power the vehicle and recharge the battery. As the belt slips, all of the accessories operate at a diminished output. The amount of electricity produced by the alternator, for instance, will fluctuate with a belt slip. This may lead the motorist to conclude that they have a bad battery or alternator when the problem is actually a worn belt or tensioner.

The check engine lightOpens in a new tab.

As you can see, the effect of a worn tensioner can be very damaging. It’s up to you to decide is it safe to drive with a badOpens in a new tab.

What Are The Most Common Signs Of Bad Belt Tensioner

What Are The Most Common Signs Of Bad Belt Tensioner

A bad belt or failing belt tensioner can give you signsOpens in a new tab.

1. Serpentine belt slipping off during startup

If the serpentine belt slips off after the engine is started or running that means the belt tensioner is no longer applying tension to keep the serpentine belt in place. With the engine off, check the belt tensioner and pulley. The pulley should spin freely without making any noise. If there is noise, then the tensioner is bad. In addition, use an appropriate belt tensioner tool and loosen the tensioner. If the tensioner feels like it is easy to move, then most likely the tensioner is probably worn.

2. Failed hydraulic tensioner

A proper working hydraulic tensioner can apply a good amount of tension. When there is a leak, the tensioner can no longer apply the needed tension to the belt. Check the tensioner for oil leakage. If there is a leak, you should replace the tensioner.

3. Growling noise

When the tensioner starts to go bad, it will start to make a loud growling noise. This means that the bearing inside the tensioner is failing and eventually it will fall apart. Sometimes when the tensioner falls apart, the pulley itself can also fall out of place. So, if you hear a growling noise, make sure to replace the tensioner.

4. Serpentine belt wearing rapidly or unevenly

There needs to be a proper belt tension for the serpentine belt to fit properly on each spinning pulley grooves such as the alternator, AC compressor, power steering pump and other. When the tension is weak, the belt can jump out of place and sit unevenly on the grooves. This will cause the serpentine belt to rapidly wear out and eventually fall out of place.

5. Loss of power and battery light illuminated

When the tensioner fails, the serpentine belt will slip off and break. When this happens, the alternator, power steering pump, and AC compressor will stop working. Since there is no belt turning the pulley, the battery light will turn on, and steering will be difficult. The AC compressor will also stop working as well.

Can Belt Tensioner Cause Squeaking

can belt tensioner cause squeaking

A bad or worn belt tensioner can cause the belt to slip at the accessories and create squealing noises, especially when it’s wet outside. This is because when the tensioner is worn out, the belt becomes loose and there is more room between the belt and the pulley which allows water to get in and produce the squealing noise.

Igor Iwanowski

I am a certified Automotive Service Excellence (ASE) mechanic since 2018. I specialize in Brake systems, dashboard warning lights, EGRs, general engine problems, EVAP and Emissions issues.

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