Serpentine Belt vs. Timing Belt

Even though a lot of people use these terms interchangeably during conversation, serpentine belts and timing belts are two different belts.

In this article, we will explain the function of both serpentine belts and timing belts. We will also discuss some of the symptoms that your car will present when these belts are failing and the effects that each can have on your car if they do fail.

Serpentine Belt vs. Timing Belt

Serpentine belts and timing belts serve very different purposes. Serpentine belts are used to provide power to peripheral components of your vehicle. Whereas timing belts are used to synchronize the rotation of the crankshaft and the camshaft. The symptoms these belts present when failing are also very different.

Serpentine Belt Explained

A serpentine belt also known as the drive belt is a belt used to transfer rotational force from the crankshaft to other peripheral components of the vehicle. A serpentine belt derives its name from the fact that it is a long continuous belt that wraps around several drive pulleys, in similar fashion to a serpentine wrapping around its prey.

Serpentine belts provide power to the peripheral devices of a vehicle since it is wrapped around a pulley that is rotated by the engine’s crankshaft.  As the engine runs, it rotates the crankshaft thereby rotating the attached pulley which causes the serpentine belt to rotate.

In addition to wrapping around the pulley powered by the crankshaft, the serpentine belt wraps around other pulleys that drive your peripheral devices like the air conditioning compressor, the alternator, the power steering pump and in some instances even the car’s water pump.

As the pulley propelled by the crankshaft rotates, the serpentine belt transfers this rotational force generated by the crankshaft to all of the other pulleys causing them to rotate in unison. As the pulleys rotate, they provide engine power to the compressors and pumps that control the systems that we named.

Timing Belt Explained

The timing belt derives its name from its function since the timing belt literally keeps the engine in proper timing.

The timing belt synchronizes the rotation of the camshaft and crankshaft. As the camshaft and crankshaft rotate, they cause the pistons to rise and fall and the engine’s valves to open and close.

These events must occur in a well-orchestrated rhythm to prevent catastrophic engine failure and the timing belt is the conductor of the symphony.

The timing belt is a rubber belt with nylon cords that reinforce the belt. The timing belt also has “teeth” on the underside of the belt that fits into the teeth of the camshaft pulley and the crankshaft. The camshaft has lobes which open and close the exhaust and intake valves in sync with the piston.

The engine’s pistons are attached to the crankshaft and the crankshaft is also connected to the engine’s flywheel. As the camshaft opens and closes the intake valves the mixture of air and fuel is burned and resulting in mini ”explosions” within the engine’s combustion chamber.

As these mini-explosions occur, the resulting force causes the piston to move downward. During the engine’s exhaust stroke, the piston is moved upward. The constant upward and downward movements of all of the pistons causes the crankshaft to rotate.  

The crankshaft is also connected to the flywheel, as the crankshaft creates linear energy from its movement upward and downward, the flywheel converts the linear energy into rotational energy that provides power to the drive wheels of the vehicle.  

All of these essential movements must occur in a very specific time to prevent the engine’s internal components such as the pistons and valves to crash into one another. The timing belt ensures that these movements occur in the proper timing.

Symptoms Of A Failing Serpentine Belt

Before a serpentine belt fails, there are often some subtle and not so subtle symptoms that may present themselves as you are driving your car.

Squealing Belt

Just as many other belts in our cars, the serpentine will often make a squealing noise as it becomes worn.

The best way to describe this noise is that it sounds like a chorus of crickets on steroids coming from under the hood of your car. Sometimes this slipping noise can become louder, or the cadence of the noise increases if you step on the gas pedal.

Serpentine Belt

Often this slipping noise is caused by a worn serpentine belt because the belt is slipping as it rotates on the pulley. Internal combustion engines create a large amount of heat as a byproduct.

After a while, constant exposure to the heat generated by the engine causes the belt to stretch and loosen. As the belt rotates on the pulley while in this loosened state, the squealing noise is created.

Dim Lights

Another symptom a serpentine belt is failing is dim lights. In some instances, you may notice that your interior lights are dim or that the headlights of your car are dim when the car is idling but they mysteriously become bright again once you begin driving again.

Or you may notice that these same lights are dim while idling and that they become bright if you slightly step on the gas pedal while stationary.

While this can also be caused by the failure of other components, in some instances it is caused by a failing serpentine belt. A failing serpentine belt is usually the cause of this condition when the alternator pulley is one of the pulleys that are driven by the serpentine belt.

As previously described, as the belt ages it can become stretched and once this happens it may not drive the alternator pulley at the same rate of speed which can cause the alternator to generate less power. As a result, you may see that the lights in your car are dimmer than usual.

Flickering Lights

Flickering lights can also be a sign of a failing serpentine belt. Since the lights and other accessories are often powered by the alternator, flickering headlights can also arise similarly to the dim lights when the serpentine belt is not operating as designed.

Engine Overheating

Another symptom can be the vehicle overheating or running hotter than normal. This will usually occur in vehicles that use a serpentine belt to power the water pump. The water pump is used to circulate coolant through the engine to dissipate heat.

Where the serpentine belt provides insufficient rotational force to the water pump, it may decrease the water pump’s ability to adequately circulate coolant through the engine which causes the vehicle to run hotter than normal or to overheat.

Cracking Of The Belt

If the belt hasn’t deteriorated to the point where it has loosened you may not experience some of the other symptoms that we have discussed, but a visual inspection of the belt can also uncover a failing serpentine belt.

As a serpentine belt ages, the rubber that the belt is made out of can begin to deteriorate as it is exposed to the engine’s heat. As the rubber deteriorates, you may notice that the belt has developed a series of cracks along the ridges of the belt.  

Snapping Of The Belt

One of the more detrimental failures of serpentine belts that can occur is the belt snapping. As the belt ages and begins to deteriorate while under tension, the belt can snap.

When this happens, the serpentine belt is no longer one continuous loop that connects the crankshaft pulley to the pulleys of the peripheral components. When this occurs, one of the more noticeable symptoms will be a loud thumping noise that is created as the ends of the belt flap around in the engine bay.

Some other symptoms could be the car stalling, lights no longer working, power steering no longer working or the air conditioning no longer being cold or blowing.

Effects Of A Failed Serpentine Belt

Some of the symptoms of a failed serpentine belt and the effects of a failed serpentine belt are often one in the same.

When a serpentine belt ultimately fails, your vehicle may overheat and even shut off while you are driving. If the serpentine belt is used to power the power steering pump, you may also notice that the steering wheel becomes increasingly difficult to turn since the pump is no longer operating as designed.

You may also notice that the air conditioning compressor is no longer functioning once the serpentine belt fails if the a/c compressor is connected to the belt.

While a failing serpentine belt may not render your vehicle inoperable, a serpentine belt that has failed often will.

Symptoms Of A Failing Timing Belt

While the failure of either a serpentine belt or a timing belt is undesirable, the results of a failed serpentine belt can sometimes be catastrophic while the effects of a failed timing belt are almost always catastrophic.

In many instances, the signs of a failing timing belt can be a bit more subtle than the symptoms of a failing serpentine belt. In other instances, the timing belt may fail with little or no symptoms. Below you will find some common symptoms of a failing timing belt.

Decreased Oil Pressure

If your car has an oil pressure gauge in the instrument cluster, as the timing belt begins to fail you may notice that the oil pressure is not as high as it used to be.

In some cars, this is caused because the oil pump is dependent on the timing belt to function properly. Where the oil pump is not operating optimally because of the timing belt or other conditions, a decrease in oil pressure may occur.

Engine Misfires

Another symptom of a failing timing belt can be engine misfires.

Where the timing belt has deteriorated to the point that it has become loose or is missing a tooth, the timing of the engine’s cylinders opening, and closing can be impacted. The mistiming of when the cylinder opens and closes can cause misfires.

Rough Idling

While rough idling can be a symptom of the failure of other components or sensors, it can also be a sign of a failing timing belt. In some instances, as the timing belt wears and begins to deteriorate, the teeth can separate from the belt.

When these teeth separate from the belt, they may become lodged between other rotating components of the engine’s internals and cause rough idling.

Excessive Smoke In Exhaust

Excessive smoke in your car’s exhaust can also be a sign of a failing timing belt. Since the timing belt is used to synchronize the timing of the rotation of the camshaft and crankshaft as described previously, a failing timing belt can throw off this rhythm.

As the rhythm of these two shafts is disrupted it can also impact the timing of the engine’s intake and exhaust stoke. When this occurs, you may notice an excessive amount of smoke emanating from the tailpipe.

Effects Of A Failed Timing Belt

Bent/Broken Valves

A very common effect of a failed timing belt would be bent/broken valves. When the timing belt fails and breaks, it can no longer synchronize the movement of the camshaft and crankshaft.

When these two shafts are no longer rotating in proper time, the valves and pistons will make contact with one another. When these two components make contact the result can be bent or broken valves.

Damaged Pistons

Piston damage can also occur when the timing chain fails, and the pistons and valves collide.


While both serpentine belts and timing belts are found in many vehicles their functions are completely different. A serpentine belt is used to power the car’s peripheral components while a timing belt is used to ensure that the camshaft and crankshaft rotate in proper timing.

The failure of a timing belt will more than likely lead to an engine replacement, or an engine rebuild while the failure of the serpentine belt may not have the same impact.

While serpentine belts and timing belts have many differences, they have one thing in common, they should both be changed at the manufacturer’s recommended intervals to prevent damage to your vehicle.

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