Serpentine belts 101
By Allstate
Last updated: October 2022
If you’re not quite sure what a serpentine belt (sometimes referred to as a fan belt or accessory belt) is or what it does, you’re not alone. Many people don’t know what this vital part of your car’s engine is responsible for, how to maintain it or when it needs to be replaced. It’s also helpful to recognize the signs that you may have a worn or bad serpentine belt before it breaks and causes all sorts of issues. Finally, we’ll explain the process of replacing a serpentine belt, how much it costs and whether it’s covered by a typical car insurance policy.
What is a serpentine belt?
A serpentine belt is one long rubber belt along your car’s engine that provides power to many vital components in your car like the alternator, power steering pump, air conditioning and sometimes the water pump, according to Firestone.
How does a serpentine belt work?
The serpentine belt uses pulleys and a belt tensioner to transfer power from the engine crankshaft to all the other components, says TheDrive.com. There is only one serpentine belt on most modern cars, and it is constantly moving whenever your car is running.
What is a belt tensioner?
Most cars today have a self-tensioning device called a belt tensioner (or an automatic belt tensioner), according to Firestone. This device holds the correct amount of tension on the serpentine belt so that it can run properly. Most belt tensioners have an internal spring and pulley to apply the proper amount of force to keep the serpentine belt tight and prevent it from slipping, squealing or running hot.
Serpentine belt vs timing belt
A timing belt ensures that your engine is running smoothly, explains Firestone. Timing belts ensure a vehicle engine’s camshaft and crankshaft are rotating at the same time, so that the pistons and valves don’t hit one another. In some cars, there may be what’s called a “timing chain” instead of a rubber belt, which essentially does the same thing.
Serpentine belt maintenance
For most cars, it’s recommended that you get the serpentine belt inspected once your car reaches 60K miles, explains AutoZone. It’s also important to perform visual and audible inspections for wear and tear before that milestone. And because every car is different, your vehicle’s owner’s manual should have the proper service intervals to get it checked.
How often does the serpentine belt need to be replaced?
By the time most cars reach 90K miles, it’s recommended to replace the serpentine belt (regardless of the appearance) to reduce the chances of it breaking, explains AutoZone. A broken serpentine belt can be dangerous while driving and could cause serious damage to your engine. Again, since every car is different, it’s recommended you check your specific vehicle’s owner’s manual for the manufacturer’s recommendation around replacing the serpentine belt.
Bad serpentine belt symptoms
You should become familiar with the following six symptoms that may show signs that your serpentine belt is beginning to fail and may need replacement, according to The Car Care Council:
- Squeaking, squealing or chirping sound from under the hood of the car
- Check engine light or battery light is illuminated on your dashboard
- A/C isn’t working
- Power steering isn’t working
- The engine’s temperature is high or overheating
- Smell of burnt rubber
Additionally, if you do a visual inspection of the serpentine belt when the car is turned off, you can look for these signs of wear, according to Consumer Reports:
- Cracks, splits or fraying
- Signs of glazing on the belt’s sides
- Separating layers or missing chunks of grooves when you twist the belt
If you see any oil or coolant saturation on the belt, Firestone notes that this means it's definitely time to replace the belt and fix those leaks.
How much does it cost to replace a serpentine belt?
A professional mechanic may charge you between $75 and $120 in labor to remove your old serpentine belt and replace it, according to AutoZone. Additionally, you’ll need to pay for the replacement belt itself, which starts around $20, but can vary in price based on what kind of car you drive and the brand of the replacement belt.
Can I replace the serpentine belt myself?
Make sure you understand the process before you begin if you’re considering doing the replacement yourself, warns AutoZone. Since you’ll likely only replace your serpentine belt once during the life of your car, it’s generally recommended to take your car to a professional mechanic. You can do a lot of damage to your vehicle if you drive on the road with an improperly installed serpentine belt.
For replacing the serpentine belt, all you need is a new serpentine belt and belt tensioner tool, according to AutoZone. For most DIY mechanics, the toughest part of the entire process is getting to the serpentine belt in the first place. It’s recommended that you take lots of pictures with your phone before you remove the old belt. This will make it easier to remember how to route the belt when replacing it.
The first step is to remove the old serpentine belt using the belt tensioner tool, says AutoZone. They caution you to take the belt off carefully, making sure you don't damage the nearby network of pulleys and other components. Next, thread the new serpentine belt into position, cranking the tensioner tool and slipping the belt over the tensioner pulley.
Safety considerations
When you are working on your own car, having the appropriate safety gear is just as important as having the right tools. The experts at NAPA recommend the following for every DIY mechanic:
- Jack stands
- Safety glasses
- Fire extinguisher
- First aid kit
Make sure your toolbox contains everything you need to make necessary repairs — and protect your safety.