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The serpentine belt transfers power to your vehicle’s many components. Replacing a worn or cracked belt can make your engine run more smoothly and save you from potentially costly repairs.

What is a Serpentine Belt?

The serpentine belt is aptly named for the way it snakes around the pulleys inside the engine bay. This long, winding rubber belt powers many of the important systems of your vehicle by transferring power from the engine’s crankshaft to the accessory pulleys. These pulleys rotate to power components like the alternator, power steering pump, and air conditioner. In some cars, it even powers the water pump in the cooling system.

Belts and Tools to Do the Job Right

How to Replace Your Serpentine Belt

1

Note the placement of belt

Serpentine belts have that name for a reason. They 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. 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 unroute the belt carefully, taking care not to disturb or damage the network of pulleys and peripherals.

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 they 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 to 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. Get the parts you need from AutoZone.

Why is My Engine Squealing?

In all likelihood, it’s probably not your engine that’s responsible for all the racket. Squealing from the engine bay probably comes from a worn out belt. It could be a drive belt or serpentine belt. When rubber belts start to wear out, they slip and slide. This makes a squeaking or squealing sound. Ever notice how your tires screech and squeal when they lose grip? It’s the same thing with your car’s belts. When you hear this sound, you’ll want to get the belt replaced immediately. If the belt is worn enough to slip, it’s going to start wearing out faster. If it breaks, the broken belt could flip around in the engine compartment and potentially cause major damage to your vehicle.

What Happens When the Serpentine Belt Goes Bad?

Serpentine belts don’t need to be replaced particularly often. Most last for around 50,000 to 100,000 miles. Consult your owner’s manual maintenance section for replacement intervals. When you notice one of these four signs, it’s time for a new serpentine belt: Serpentine belt transfer power from the engine’s crank shaft to the engines alternator, power steering pump, smog pump*, and air conditioner compressor. This one belt provides power to all the vehicles components. Some vehicles have a dedicated belt for the alternator just in case the serpentine belt should break. The vehicle can continue driving until it reaches a safe place to stop.

  • Squealing from power steering or air conditioning: The serpentine belt controls peripherals such as power steering and air conditioning, and these devices take a lot of torque from the belt to turn, so if you turn the wheel, or turn on the AC and hear squealing, the chances are, your belt has worn.
  • Wear and tear: If a visual inspection of the serpentine belt reveals significant wear and tear, including cracks, separation, or damage, it’s time for a new belt.
  • Squealing noise under the hood: This may signal that the belt is slipping. Sometimes a new belt is not needed. The belt is kept tight through the belt tensioner. The tensioner is a self-adjusting pulley that maintains pressure on the belt to reduce slipping. At times, the bearings in the tensioner pulley become worn. This causes the squealing noise. Check these bearings when performing a belt change.

*if equipped

How Long Do Serpentine Belts Last?

Serpentine belts can last for years and might only need to be changed once or twice over the life of the vehicle. The recommended industry standard is to inspect your belt at 60,000 miles for wear & tear and replace if necessary, and replace every 90,000 miles regardless of the appearance in order to reduce the chances of a breakdown.

Like anything else in your vehicle, it is not indestructible and will eventually falter. If you keep your car long enough, or if it’s an older model, be prepared to replace it as belts will succumb to heat and friction over time. The best way to determine when yours should be replaced is to check your owner’s manual for the service interval.

What Does a Worn Belt Look Like?

Wear and tear, as well as extreme temperatures, will take a toll on the serpentine belt at some point. Years of use could cause the belt to crack or wear unevenly. It’s a good idea to periodically check the belt or have a mechanic inspect it for you during routine car maintenance. Keep in mind that serpentine belts don’t show cracks like their predecessors. Newer belts wear more like tires, so you’ll need to look for rib material deterioration. Other signs of problems are damaged ribs or rib separation. Your mechanic can let you know when to replace the serpentine belt or how many miles it has left.

Worn serpentine belt

Look on the inside of the belt (the ribbed side that touches the pulleys on the alternator, water pumps, and other engine accessories). If you notice the ribs cracking, the ribs are worn away, or you notice any other substantial belt wear, it’s time to change the belt.

If you have a recurring issue where your belt frequently breaks, or it breaks long before it should have, it is possible that an issue like pulley drag, obstruction or debris in the engine bay, or contamination of the belt and pulley from leaking oil or coolant.

Listen for Clues

You may not have to lift the hood and look for visible evidence of a worn-out serpentine belt. Sometimes, your ears can be your ally. Like many other parts and components on your vehicle, when the serpentine belt nears the end of its life, you may start to hear strange noises. Belt problems aren’t limited to wearing out, breaking, or contamination of the pulleys and belt. Some may slip, causing significant problems with your vehicle. When this happens, you may hear a chirping or squealing sound. This could also indicate that the belt has stretched out and that there is a tension issue. The pulley system that operates the mechanism of the belt may also be failing.

What Happens When the Belt Breaks?

If you’re like many other drivers, you’ve probably driven farther than you should when parts or systems are going out. With some components, you can get away with keeping your car on the road for a little while. However, if your serpentine belt breaks completely or falls off, you won’t have any option but to replace it.

When your belt fails, everything that it is driving stops functioning. In most cases, this is the alternator, water pump, and power steering pump. Usually the first one you feel is a lack of power steering. Your battery light will also illuminate, as your alternator has stopped working. Lastly, your engines temperature will very quickly rise, as your water pump has stopped working. It is extremely important to understand that the moment you have seen any of these symptoms, pull over immediately! Quickly get your vehicle into a parking space away from congestion if you are not on the highway. If you determine that your belt has broken, you cannot continue to drive the vehicle. The vehicle will overheat within a matter of minutes, and at that point, you risk the possibility of warped heads, blown head gaskets, and damage that is far, far worse than a tow bill.

The Cost of Replacing the Belt

If you’ve got a bad serpentine belt, don’t hesitate to get a new one. This will give you the peace of mind you need to get back on the road safely. Just think, the next time you purchase a belt may be the last time you’ll ever have to do so on that vehicle. More good news: serpentine belts are inexpensive compared to other car parts and components. A professional mechanic will normally charge between $75 and $120 in labor to remove the old belt and replace it with a new one. If you’re thinking about doing this work yourself, make sure you understand the process. You don’t want to drive around with an incorrectly installed serpentine belt. If you need help changing the belt, search through our list of local Preferred Shops in your area.

When you’re in the driver’s seat of your vehicle, you probably don’t spend a lot of time thinking about the serpentine belt. As you understand more about how this rubber component powers your vehicle, you’ll start to appreciate it more. Keep your eyes and ears out for the signs of a damaged belt so you’ll know when you need to remove it and put on a new one. You can then continue driving safely, and your car’s reliability will improve.

Advice, how-to guides, and car care information featured on AutoZone.com and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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