Belts on your vehicle are essential for connecting components and ensuring that everything runs in harmony. This is true of the serpentine belt, timing belt, and any other belt systems your vehicle has.
Typically, you won’t even notice these belts until you start to encounter some problems. For example, many people don’t know what a serpentine belt does until it’s too late.
Serpentine belts transfer power from alternators to several components in your vehicle, like the air conditioning and power steering system.
Unfortunately, it’s hard to notice a failing serpentine belt until these systems start to not function properly. Plus, if you’re unsure about what the serpentine belt does you might try to fix other components before addressing the root of the problem.
The good news is that we’re here to help. Learn everything you need to know about serpentine belts down below.
What Is a Serpentine Belt?
A serpentine belt, sometimes referred to as a fan belt or drive belt, is a long belt that connects to several components in your vehicle. Serpentine belts are made of a durable, rubber-like material that stretches from the alternator to components like the water pump, air conditioning, and power steering components.
Most serpentine belts are made with reinforced rubber that can last for several years and thousands of miles.
Depending on your vehicle, serpentine belts may also have some other enhancements. Examples include a belt tensioner or an idler pulley. These can be spring-loaded or hydraulic. In some cases, they may even be manual but this is less common on vehicles manufactured after the year 2000.
How Many Serpentine Belts Does an Engine Have?
Most engines have one serpentine belt because it’s a single, continuous rubber belt.
However, there have been some variations over the years and some manufacturers have used two serpentine belts to connect every system. This is true in a handful of BMWs as well as the Ford Taurus SHO. Some Nissan vehicles, like the Nissan Maxima DOHC from 1995-1999, also come equipped with two serpentine belts.
That said, this design isn’t common. Vehicles with more than one serpentine belt are usually an exception rather than a rule. Still, always consult your vehicle’s owner’s manual to better understand your vehicle’s serpentine belt configuration.
Where Is the Serpentine Belt Located?
Serpentine belts are found on the exterior of your vehicle’s engine, sometimes underneath an engine cover.
You’ll know you’ve found the serpentine belt when you find the alternator and the belt that’s connected to it. The alternator is located towards the front of most engines and it’s bolted onto it, which makes it an exterior engine component. Alternators are usually large, cylinder-like components and they’re hard to miss.
Serpentine belts are connected to the alternator, so once you find it you’ll find the serpentine belt. You can also look for components like the water pump, power steering system, and air conditioner because the belt also connects all of these components.
Ultimately, the location of the serpentine belt depends on the make and model. Some performance-focused vehicles may have different variations and some manufacturers like BMW are known for using multiple serpentine belts.
How Long Do Serpentine Belts Last?
Serpentine belts can last for decades if the vehicle isn’t driven often. In fact, it’s not uncommon for serpentine belts to last for the extent of a vehicle’s lifespan if you never reach 100,000 miles. This is because the reinforced rubber is durable and resistant to decomposition.
On the other hand, if you run the miles up on your vehicle the serpentine belt will fail. Unfortunately, it’s inevitable because it’s a wear item. Have your serpentine belt checked after 60,000 miles to be safe, but most belts will last for about 90,000 miles before needing to be replaced.
What Does a Serpentine Belt Do?
Serpentine belts have one role in most vehicles. This is to transmit rotational energy from the crankshaft to the vehicle’s alternator and accessory components like the air conditioning system or power steering system. The serpentine belts spin to generate this electricity, which it can then bring to other pulley systems in your vehicle.
Accessories in every combustion vehicle have pulleys that provide power for them to function. Think of the serpentine belt as the central pulley that connects all of these various other pulleys and supplies them with power from the crankshaft.
When the serpentine belt spins, it causes the other pulleys to spin as well. Everything spinning together makes for a happy engine with functional accessories.
Many serpentine belts don’t work alone and have components attached to them like the idler pulley or belt tensioner.
What Does an Idler Pulley Do?
Idler pulleys press against the rear side of the serpentine belt. The idler pulley creates enough of a wrap angle on an accessory’s pulley to prevent the belts from slipping. Essentially, they’re small components that ensure that belts don’t come out of contact with one another.
What Does the Belt Tensioner Do?
A belt tensioner is a nifty component that modern vehicles have to ensure that tension remains consistent. It also ensures that the level of tension is ideal for serpentine belt performance, so you don’t have to worry about adjusting the tension manually or making any changes to the belt.
Belt tensioners leverage an internal pulley and spring to accomplish this task.
Unfortunately, many older vehicles don’t have belt tensioners. In these cases, you have to set the tension of the belt manually. Always have a professional adjust the tension manually if you’re unsure about the process to avoid any complications. Setting the tension wrong can cause a chain reaction of engine problems and damaged components.
Signs of a Bad Serpentine Belt
Serpentine belts will fail after 50,000 to 100,000 miles depending on the belt and type of vehicle. Therefore, it’s important to recognize the signs of a bad belt. Bad serpentine belts will cause damage to essential engine components, like the alternator, so replacing the belt is important the second you notice any issues.
We list the signs of a bad serpentine belt below.
- Squealing or chirping noises.
- Vehicle performance loss.
- Visible signs of belt wear.
- A check engine light.
Learn more about each of these signs below.
Squealing or Chirping Noises
Have you ever heard an engine sound like it’s screaming when it starts? If so, that’s probably a bad serpentine belt. It’s one of the most obvious signs of a bad serpentine belt and you can hear it loud and clear from your cabin.
Other people around you will also hear this noise because it’s very loud. It may sound like a loud squeal or a chirping bird. You’ll usually notice this sound when you start the engine and it gets up to speed.
Vehicle Performance Loss
One of the more serious problems that a bad serpentine belt will cause is a decrease in engine performance. The serpentine belt connects a lot of systems, so it’s not uncommon for many of them to fail as the belt goes bad.
Some examples of vehicle performance loss that happens because of a bad serpentine belt include:
- Heavier steering as less power reaches the power steering pump.
- Dead batteries or batteries that can’t hold a charge.
- The air conditioner not working properly.
- Your engine stalling.
- A reduction in acceleration at low RPMs.
These are only a handful of performance losses you can expect to have with a bad serpentine belt.
Visible Signs of Belt Wear
Pop the hood and take a look at the serpentine belt. You can find it attached to the alternator and several pulley systems in your engine bay. When examining the belt, look for signs of wear and tear. These include cracks, glazing, and frayed rubber fragments. In serious cases, you may even notice large chunks missing from the serpentine belt.
A Check Engine Light
Nobody wants to get a check engine light, but it’s a helpful tool that indicates something is wrong. If the check engine light comes on and you notice a reduction in power, visible belt wear, and hear squealing noises, it’s an indication that your serpentine belt is failing.
Check engine lights can also mean other problems, so make sure you diagnose the problem properly with an OBD2 scanner. These tools will help you learn about the exact issue that’s causing a check engine light.
Make sure you replace your serpentine belt once you notice any of these problems to avoid damage to integral engine systems like your alternator, battery, or power steering pump.
How to Replace a Serpentine Belt
Serpentine belts are tricky to replace because they snake through the engine. Learning about how to replace one takes time and requires a lot of careful consideration. For this reason, we always recommend bringing your vehicle to the shop if you plan on replacing a serpentine belt.
That said, we list the steps below for anyone who wants to replace their vehicle’s serpentine belt.
1. Take Pictures
The serpentine belt snakes around the engine and connects many pulleys. Knowing how the serpentine belt is supposed to be placed is important so that you place the new one on properly. Messing this step up almost guarantees severe problems. So, take pictures of how the belt connects to different pulleys across the engine.
2. Unthread the Belt
Serpentine belts are under a lot of tension, so you need to unthread the belt before you remove it. Failing to do so can result in a sudden snap that will hurt you. Use a belt tensioner tool, ratchet, or breaker bar to remove tension from the belt before you remove it. Most serpentine belt sockets are ½” or ¼”.
Then, remove the belt slowly. Make sure you don’t damage other pulley systems or components as you remove the belt.
3. Check for Damage
Serpentine belts run across the length of a vehicle’s engine bay and connect a lot of components. When they fail, many things often fail with them. Therefore, make sure you check for damage to other components before just slapping a new serpentine belt on them.
Some signs of damage to look for include the following:
- Spin the idler pulley and tensioner pulley and listen for any noise. They should be quiet and spin freely.
- Check for oil leaks.
- Use a straight edge to check the alignment of other belts and pulleys.
- Check each pulley for noise or movement. Leaving pulleys that don’t spin properly will damage the systems they’re attached to and cause problems for your new serpentine belt.
Also, make sure you check the serpentine belt for damage. Depending on the type of damage you may have a misalignment problem on your hands. This needs to be addressed before adding a new serpentine belt.
4. Install the New Belt
Install the new belt by threading it into the correct position. Then, crank the tensioner and slip the belt over the tensioner pulley to ensure that it’s in the right place and properly tensioned. As you thread the serpentine belt make sure you’re threading it properly by making sure it’s centered.
5). Run the Engine for 60 Seconds
The last step is to run the engine for at least 60 seconds. Doing so will let you know if you installed the serpentine belt properly because you’ll hear noises or notice other problems. After 60 seconds you’ll know one way or the other if your serpentine belt replacement was effective.
Make sure you follow each of these steps carefully when replacing a serpentine belt to avoid any problems.
How Much Does a Serpentine Belt Replacement Cost?
Serpentine belt replacements can cost $30 to $200 depending on how it’s done. Most serpentine belts only cost about $30, so if you replace the belt at home it will only run you $20 to $30 and a few hours of your time.
However, mechanics will charge for labor and that can be $50 to $120 per hour. This increases the cost to about $200 with components and labor.
If any other belts are also worn down the price will also Increase. Still, it’s worth checking them and replacing them all at once to avoid problems down the line.
Get Back on the Road Today
Serpentine belts are one of the most important pulley systems in your vehicle. Without a functional serpentine belt, your accessories won’t get power and your engine may stall. Plus, the battery may die and your car won’t even start. This is why it’s important to understand how a serpentine belt works and when to replace it.
Thankfully, as long as you pay close attention to your vehicle and practice regular engine maintenance, you shouldn’t have any issues with your serpentine belt.
