What Is a Serpentine Belt and How to Replace It?

A serpentine belt is an important part of your vehicle’s engine block, but do you know what a serpentine belt really is? And what does a serpentine belt do? Where is the serpentine belt, and how long does your serpentine belt last? Read on to learn more about this vital piece of your vehicle that is responsible for powering your alternator, power steering pump, and air conditioning compressor.

What is Serpentine Belt?

A serpentine belt is a long rubber belt that transports power to your alternator, power steering pump, and air conditioning compressor. In some cases, it also supplies power to your water pump. It’s a long, winding rubber band of sorts that is attached to your crank pulley. Starting from there, it makes its way around your engine block, delivering power to all of the aforementioned vehicle systems.

In most cases, it features a serpentine belt tensioner that ensures your serpentine belt is at the optimum tension to efficiently move power around your engine blow.

You may have heard a serpentine belt referred to as a fan belt or accessory belt. This is because vehicles used to have multiple drive belts that connected the engine to the accessories (such as the radiator fan).

But modern vehicles (usually) just have one belt that winds through multiple pulleys to power all the accessories.

While using just one belt is the most efficient and reliable option, it also means that when your car’s serpentine belt breaks, everything stops working! You’ll lose power steering, the A/C will quit, your battery will eventually die, and the engine might overheat. Plus, it could also damage the engine accessories it controls.

Serpentine Belt Diagram

What does a Serpentine Belt Do?

Well, it won’t keep your pants up, but it does transport power to your vital automotive components. The serpentine belt is one long, snaking, winding belt that keeps your alternator, power steering pump, air conditioning, and in some cases, your water pump running smoothly and effectively.

Serpentine Belt vs. Timing Belt

Don’t get confused a serpentine belt is not the same thing as a timing belt. The serpentine belt and timing belt have very different functions in your vehicle.

The timing belt is located inside the engine and keeps the crankshaft and camshaft in sync. This ensures that the engine intake and exhaust valves open and close in time with the pistons so the engine runs smoothly.

The serpentine belt is what keeps the engine accessories running smoothly and efficiently. It connects the engine crankshaft on the outside of the engine to all of the engine accessories.

You can easily tell the difference between the two when you look at the grooves. A timing belt has horizontal “teeth” designed to fit the cogwheels of the crankshaft and camshaft. A serpentine belt has multiple V-shaped grooves that run vertically along the belt.

These belts often need to be replaced around the same time, so ask your mechanic or consult the owner’s manual to see if you need to replace your timing belt too.

Related: What is Timing Belt?

How Often Does A Serpentine Belt Need To Be Replaced?

Serpentine belts are built to last much longer than before because of advancements in rubber technology. Under ideal conditions, a belt should stick with you for an average of 60,000 to 100,000 miles. Pretty impressive.

However, some belts are manually tensioned and may need to be adjusted. Others have a self-tensioning mechanism that can experience wear over time and may need to be serviced. One thing to remember: in most cases, if the belt breaks, the vehicle will stop running.

7 Symptoms of a Bad Serpentine Belt

A bad serpentine belt is not something you can just put off and wait to deal with. The entire functionality of your vehicle may be compromised when your belt is worn, damaged, cracked, or snapped.

1. No Air Conditioning

A malfunctioning air conditioner can be attributed to a lot of things. Since the serpentine belt keeps the air conditioner functional, a bad serpentine belt will take that function away from it. If you turn on your air conditioner and see that it does not blow out cool air from the air vents, this could possibly be due to a bad serpentine belt.

2. Squealing Sounds

If the front area of your vehicle makes squealing sounds, then your serpentine belts might be misaligned or slipping. Sometimes it might just take a realignment or proper tensioning of your serpentine belt to fix this problem.

In other cases, the belt is probably damaged and will need to be replaced.

3. No Power Steering

The serpentine belt allows the power steering system to function properly. Power steering is what gives drivers the ability to smoothly steer their vehicle without needing to apply too much arm strength.

If you have a bad serpentine belt, then it will be harder to move the steering wheel to steer your vehicle. This issue could also be caused by low power steering fluid. While you’re under the hood, check to make sure the power steering reservoir has the recommended level of fluid.

4. Overheated Engine

The serpentine belt is what activates the water pump which helps cool the engine. If you have a damaged or worn serpentine belt, then it won’t be able to activate the water pump. This means that your engine will begin to overheat since it cannot be cooled down anymore.

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You will see this happening as the temperature gauge on the dashboard shows the needle moving toward the red zone. Don’t let this continue for too long or else your entire engine could get damaged.

5. Visible Cracks on Belt

The serpentine belt is easy to access in most cars. If you want to know if your belt is bad, simply open the hood and look at the belt for yourself. If you notice visible cracks or damage anywhere on the belt, this means the belt is bad and needs to be replaced right away.

6. Dead Battery

If you’re driving along one day and suddenly lose power, check under the hood to see if your serpentine belt is still attached. Even if you’re able to get the car started, a snapped serpentine belt will not allow the alternator to charge the battery.

Without the alternator’s charge, your car will eventually die from the electricity used by the spark plugs, the radio, and the headlights. A vehicle can often run without a working alternator for a bit of time, but not for long.

If the belt is too loose to maintain a grip on the alternator pulley, you may experience a similar symptom as a snapped belt.

7. Pulley Whine

If you start to notice a whine from the engine that changes with engine speed, you may want to have the tension of the serpentine belt double-checked. A belt that is too tight puts too much load on the bearings in each of the accessory pulleys and can often cause premature failure of those components.

One of the most common failure modes for water pumps is actually bearing failure, caused by a serpentine belt that was too tight. If you think your belt may be too tight, it’s best to address this issue as soon as possible to prevent expensive engine damage caused by overheating.

Related: What is Pulley?

What Happens to A Car When the Serpentine Belt Breaks?

Though your serpentine belt may not be prone to failing, it does wear down over time. As the belt begins to wear – or becomes damaged or contaminated – the engine accessories are not able to spin at the proper speed.

For example, the engine’s alternator is designed to power the car’s electrical system and simultaneously recharge the battery during operation. When the alternator doesn’t spin fast enough, the output will diminish, which can lead to loss of vehicle power, dim headlights, loss of electronic functions, and sometimes a dead battery.

Many engine accessories are vital to your vehicle’s performance. So, while it’s not necessarily a big deal if the serpentine belt breaks and your A/C stops working, it’s a much bigger issue if it causes your power steering or electrical system to fail.

Again, here are some of the primary consequences of a broken or worn serpentine belt:

  • A broken serpentine belt can lead to a sudden loss of power steering in your car, making your steering very difficult to turn. You don’t want this happening in the middle of a busy intersection when you’re trying to hang a right!
  • A broken serpentine belt causes the water pump to stop circulating coolant through the engine’s cooling system, causing it to overheat. This can happen at any time, if the belt decides to go out on you.
  • A broken serpentine belt also stops the car’s alternator from generating power, which is responsible for operating both the vehicle’s electrical and electronic systems. It also is responsible for recharge your battery, so if your headlights dim, the radio stops working, or your dash lights go out, your battery has probably died. And the reason may be that your alternator isn’t working because of a broken belt!

The serpentine belt should be kept in good working order, which includes servicing the tensioner and belt pulleys. Occasionally, the serpentine belt falls off and doesn’t break, simply because the tensioner and pulleys are worn, damaged, or misaligned. In this instance, replacing the belt will not be enough to solve the problem.

The underlying issues that contributed to the damage or misalignment will need to be addressed before the vehicle will run properly. Serpentine belts can also fall off if they aren’t routed correctly, or if it is simply the wrong belt for the vehicle.

How To Replace Your Serpentine Belt?

1. Note The Placement Of Belt

Serpentine belts have that name for a reason. The snake in and out of a series of pulleys and peripherals, and the path they weave through is unique to your model vehicle. To preserve the belt’s position, take a few snapshots from different angles or sketch the way it winds through the engine.

If the belt is already out of place, locate the driver’s manual or the under-the-hood placard, where you’ll find a sketch of the routing.

2. Loosen And Unthread The Belt

Before removing the belt, you’ll need to release the tensioner, which automatically keeps the belt taut while you’re driving. Tensioners usually have one of two ways to release tension. Many have a ½” square cast into the tensioner arm, in which you insert a ½” breaker bar, or Belt Tensioner Tool to relieve the tension.

For many others, you use a socket on the pulley itself to do this. Use a ratchet or breaker bar that fits into the bolt and release the tensioner. Then unrouted the belt carefully, taking care not to disturb or damage the network of pulleys and peripherals.

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3. Check For Damage

After removing the belt, inspect it for signs of damage. Many belts wear out over time, but some wear down due to misalignment or other issues. Misalignment won’t resolve itself when you replace the belt, so determine whether this is a problem.

Look for disintegration along the edges and separated ribs, both of which are signs that you have misalignment on your hands. Use a straightedge to make sure the pulleys are aligned correctly, and then remove any old dirt and grime from the pulleys.

This is a good time to look for oil leaks, too. Oil can increase wear on serpentine belts. Most importantly, take the tensioner pulley and any idler pulleys (these are pulleys that do not drive anything, like Power Steering) and give them a spin. Listen carefully.

They should spin freely and make no noise. Grab each pulley and check for any side to side, or in and out movement. Any excessive movement of any of these pulleys, or noise, and should be replaced. If these pulleys fail while on the vehicle, your belt will fall off, and you will be running without a water pump (in most cases), power steering, and an alternator, so check them carefully!

4. Install The New Belt

Replacing the serpentine belt is as simple as threading it into position, cranking the tensioner, and slipping the belt over the tensioner pulley, or nearest pulley up top. Belt tensioners are mostly spring tension. Once installed, the spring retains pressure on the belt.

Once on, make sure the belt is completely on and centered on each pulley very carefully. Then, start the engine. Let the engine idle for at least 60 seconds as you make sure the serpentine belt is working correctly.

Replace any other parts or coverings you’ve removed before taking your vehicle for a spin. A serpentine belt replacement is an essential part of routine auto maintenance, but it doesn’t have to be difficult.

Serpentine Belt Replacement Cost

A typical serpentine belt starts at around $25 and goes up to $75 at most. If you know some car repair basics, you could change the belt yourself, and it may save you paying labor charges somewhere between $75 and $120. Altogether, you’re looking at around $100 to $195 to replace your serpentine belt.

It shouldn’t take more than an hour (two at the most) to repair this simple problem. It depends on the model of the car and how easy it is to get to the serpentine belt within the vehicle’s framework.

Should I Replace the Belt Myself?

There are repairs that you should always leave to the professionals for safety’s sake, but this is not one of those situations. If you have a reasonable grasp of mechanics, YouTube will fill in the gaps for you. If you’re confident that you know what you’re doing, this is an ideal solution. If not, get help.

Considering that it can save you a fair amount of money and that it’s not a complicated task, we’re fine with recommending that average DIYers give it a try for themselves. The chances are that you’ll be pleasantly surprised at what you’re able to accomplish with your drive belt replacement.

Can I Drive My Car with a Bad Serpentine Belt?

It is a question that we hear frequently. There are cases where you might be able to drive your car in an emergency, but we would prefer to adopt a more cautious approach.

If the belt’s snapped, it might be difficult, if not impossible, to steer the car. If the belt’s starting to fray, it won’t be long before it snaps, so it’s better to replace it.

Do the right thing and call your mechanic straight away. The consequences of not doing so could cost you dearly later. What happens if the belt snaps while you’re on the freeway? Our best advice is to stop the car and have it towed to the shop.

FAQs.

What Is Serpentine Belt?

The serpentine belt is a long rubber belt that transports power to the engine accessories the alternator, power steering pump, air conditioning compressor, and (sometimes) the water pump. You may have heard a serpentine belt referred to as a fan belt or accessory belt. This is because vehicles used to have multiple drive belts that connected the engine to the accessories (such as the radiator fan).

What Does a Serpentine Belt Do?

The serpentine belt plays an essential role in running your car’s systems. It powers the alternator, the power steering pump, the air conditioning compressor, and, in some vehicles, the water pump. The serpentine belt rotates constantly when the car is running. With a pulley system and a tensioner, the belt uses that rotational power to drive other parts to run various accessories on the car.

What Happens to A Car When the Serpentine Belt Breaks?

If a serpentine belt breaks, a car won’t be drivable and will have to be towed. If the engine runs without a serpentine belt, it might overheat as the water pump will no longer work. A broken belt can also damage other parts. If a car has a hydraulic power steering pump, the steering will become stiff.

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When to replace the serpentine belt?

How often does a serpentine belt need to be replaced? Serpentine belts are built to last—much longer than before because of advancements in rubber technology. Under ideal conditions, a belt should stick with you for an average of 60,000 to 100,000 miles.

How much does it cost to replace the serpentine belt?

A typical serpentine belt starts at around $25 and goes up to $75 at most. If you know some car repair basics, you could change the belt yourself, and it may save you paying labor charges somewhere between $75 and $120. Altogether, you’re looking at around $100 to $195 to replace your serpentine belt.

What happens to a car when the serpentine belt breaks?

If a serpentine belt breaks, a car won’t be drivable and will have to be towed. If the engine runs without a serpentine belt, it might overheat as the water pump will no longer work. A broken belt can also damage other parts.

What are the symptoms of a bad serpentine belt?

Symptoms of a Bad Serpentine Belt and Replacement Cost:

  • No Air Conditioning.
  • Squealing Sounds.
  • No Power Steering.
  • Overheated Engine.
  • Visible Cracks on Belt.
  • Dead Battery.
  • Pulley Whine.

Can you drive with a bad serpentine belt?

There are a couple of factors influencing the answer to this question, but on average, your car should be able to run between 20-90 minutes with a broken serpentine belt. The engine will overheat faster without a functioning cooling system on a hot day, so your driving window is less.

How often does a serpentine belt need to be replaced?

Serpentine belts are built to last much longer than before because of advancements in rubber technology. Under ideal conditions, a belt should stick with you for an average of 60,000 to 100,000 miles.

How do I know if I need to replace my serpentine belt?

The easiest way to know that a new serpentine belt is needed is if you hear it squealing while the engine is running. A heavy rainstorm might cause a bit of squealing, but if there are any fluid leaks, it’s time to replace it right away.

Can I replace a serpentine belt myself?

Serpentine belt replacement is easy because today’s automatic drive belt tensioners eliminate the need to loosen bolts or pry components into position for re-tensioning. Just rotate the tensioner, remove the old belt and install a new one.

Can a bad serpentine belt cause acceleration problems?

Typically, a damaged belt tensioner will not impact vehicle performance. It would cause the serpentine or drive belt to wear prematurely or to squeak – but not cause the acceleration issue.

What causes the serpentine belt to wear out?

Serpentine belt problems usually result from one of three causes: a defective belt tensioner; misalignment of a pulley; or, defective bearings in the tensioner, idler, or one of the accessories driven by the belt (including the water pump).

How long does it take to fix a serpentine belt?

It usually takes approximately thirty minutes for a mechanic to replace a serpentine belt. With the right tools and equipment, an auto mechanic can complete the process within thirty minutes to an hour.

Can a bad serpentine belt cause check engine light?

A loose or worn belt will cause ticking or rattling noises, poor engine performance, and overheating, usually triggering the check engine light.

Is a timing belt the same as a serpentine belt?

Timing Belt. Don’t get confused a serpentine belt is not the same thing as a timing belt. The serpentine belt and timing belt have very different functions in your vehicle. The timing belt is located inside the engine and keeps the crankshaft and camshaft in sync.

Is fan belt same as serpentine belt?

Sometimes called a fan belt, alternator belt, or accessory drive belt, the serpentine belt is spun by the engine crankshaft and, in turn, spins, or “drives”, the accessories. Cars of the past relied on multiple drive belts, but today’s vehicles (usually) count on just one, the serpentine belt.

Is a serpentine belt the same as a drive belt?

The serpentine belt goes by a couple of different names: accessory belt and drive belt. The belt is long and snakes through several pulleys. That’s why it’s called a serpentine belt. You can find the serpentine belt on the front or side of the engine.

What are the 3 belts in a car?

All the Drive Belts Explained:

  • Timing Belts. A timing belt, is a notched rubber belt that opens and closes the engine valves in proper timing with the pistons.
  • Serpentine Belts. Your car’s serpentine belt is a long continuous belt that drives all your engine components.
  • V-Belts.

How do you fix a squealing serpentine belt?

How long does it take to replace a timing belt?

Replacing the timing belt is an expensive service. It is an intricate, labor-intensive process that can take 4–8 hours, depending on the vehicle. But replacing the timing belt before it breaks will prevent engine damage and save you money in the long run.

What sound does a bad serpentine belt make?

As these belts wear out, they can begin to squeak or squeal. They make noise because there is not enough tension on the belt, or because the pulleys are misaligned or weak. Often, simply changing the belt will make it stop squealing. The noise isn’t usually a danger, though it does sound alarming.

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