But sometimes even the strongest belts fail and must be replaced. Knowing when to replace your serpentine belt can mean the difference between getting to where you need to be and getting nowhere as you look under your car’s hood in puzzlement.

Here’s what the serpentine belt is and how to replace it:

What is the serpentine belt?

Although some car models may have multiple drive belts, most contemporary automobiles play host to one serpentine belt. This long flat rubber strip is threaded through a system of pullies which keep your car’s crucial features running. Without the serpentine belt, your car can neither cool itself nor properly run safety features, such as power steering.

When should the serpentine belt be replaced?

Although most car manufactures include a serpentine belt check under maintenance checkups performed at certain mileage milestones, sometimes a belt can wear out sooner. If your car makes a whirring or chirping sound, turn the vehicle off and wait for the engine to cool. Look for a long black rubber belt running through your car’s engine, this is the serpentine belt.

Cracks, splits, frayed edges or glazing are all signs of a worn belt. Also look for signs of stretching or any parts of the belt soaked in oil as these could also be symptoms of a problem. Once you identify a belt in need of replacing, do not put off getting a new one.

How is it replaced?

One size does not fit all

Depending on the age and model of your car, the length of the serpentine belt can vary. Before installing a new serpentine belt into your car, be sure you have the correct size for your engine. A belt which is too small is likely not going to fit over all of the pullies whereas a belt which is too large runs the risk of falling off or bunching up.

Release the tension

One of the pulleys in the serpentine belt system has a piece called a tensioner. This pulley can be loosened and tightened accordingly to help keep the belt on or off all the pulleys. Using a ratchet or specialized tool, the tensioner can be easily loosened and the worn belt can be removed.

Tip: on older cars the tensioner is usually of a manual variety. But newer models are usually equipped with spring-loaded belt tensioners.

Find the serpentine belt diagram

Most engines have a pictograph showing the proper configuration of the serpentine belt system. This diagram should also show if there are multiple belts or special configurations for car features like your AC. Compare the diagram to your engine to get a quick understand of how it should look before you get to work.

Installing the new belt

Run your fingers along the new serpentine belt: there should be one grooved side and one smooth side. Identify the pullies with grooves as these are the pullies which should be facing the grooved side of the new belt. Carefully thread the new belt through the system of pullies according to the serpentine system diagram.

Tip: the belt does not have to be perfectly aligned with the pullies but should be close to avoid slipping off once you run your car’s motor.

Add some tension

Once the new serpentine belt is in place, adjust the tensioner to tighten the new belt over the pullies. Proceed to run your car’s engine to ensure the belt is flowing smooth through the serpentine system.