How to Put a Serpentine Belt on a Car

serpentine belt on an engine

If you've ever broken a serpentine belt and found yourself stranded with your car because it won't even start, then you probably understand the importance of learning how to put a serpentine belt on a car.

What is a Serpentine Belt?

The serpentine belt is a single one-inch thick rubber belt that winds its way around several pulleys and operates a number of critical engine components using the power of the engine itself.

What the Serpentine Belt Does

The serpentine belt uses engine power to turn the pulleys that power the following engine components:

  • Water pump, which cools the engine
  • The air conditioner
  • The alternator, which recharges your battery and makes electrical devices work properly
  • Power steering pump

Since the serpentine belt powers so many of your car's critical systems, it's important to be sure that it is in top condition.

How to Identify a Bad Serpentine Belt

If you've ever tried to start your car in the dead of winter, when the temperatures are sub-zero, then you've probably heard the loud screeching of a slipping serpentine belt. In the winter, the natural shrinking of the belt increases the tension too much and leads to the screeching sound.

However, in other situations, an old serpentine belt can degrade or get cracked, and slippage can occur. A loud screeching noise doesn't always mean that your serpentine belt is going bad; it could mean that the belt tensioner is faulty and needs replacement. You can identify whether the serpentine belt needs to be replaced by following the procedure below:

  • Open the hood and find the belt on the side of your engine (usually on the right or left).
  • Lean down close to the belt, and hold a dental mirror up to the belt so that you can see the ridges on the underside.
  • Observe whether there are a lot of deep cracks or frays in the rubber belt.

If you find that the belt is filled with a lot of deep cracks and frayed pieces, it may be a good idea to replace the belt with a new one.

How to Put a Serpentine Belt on a Car - Step-By-Step

While many people pay to have the serpentine belt changed, you can actually do it yourself and save a lot of your hard earned cash. The process can be time consuming, but it isn't complicated or highly technical. By following the steps below, you can complete this process, either to replace a failed belt or as preventive maintenance to stop a failure from leaving you stranded.

  1. First, closely examine the path that the old belt follows around each pulley. If you need to, create a diagram that shows the entire path of the belt so that there's no confusion when you're preparing to install the new belt. Also, some vehicles provide a routing diagram either under the hood or in the manual, so make sure to look for one.
  2. Insert a 3/8-inch ratchet into the hole in the tensioner arm. You'll need an extension to reach inside the hole. The 3/8-inch hole is the adjustment for loosening the belt, which will allow you to remove the entire belt from all of the pulleys.
  3. While you have the belt removed, it's a good time to double check that all of the pulleys are aligned. Misalignment can lead to faster wear, so hold a straight-edge against each pulley and make sure that they are all correctly aligned and square. Serious misalignment of the pulleys may require additional repair work by a trained mechanic.
  4. Find the tensioner - a pulley with a spring movement - and spin the pulley to be sure that it spins freely. If there is any friction in the tensioner pulley or you notice that when you pivot the tensioner arm there is some tension, you probably need to replace the tensioner assembly as well. While you may want a mechanic to do this, tensioner assemblies are available at auto parts stores and are not too difficult to replace.
  5. Check for leaky oil. If the serpentine belt area seems especially covered with oil, you may have an oil leak in the vicinity. Oil can quickly degrade rubber, so you'll want to search for the leaky engine seal and repair the problem before installing a new belt, or you'll find that it'll need replacement again prematurely.
  6. Before installing the new belt, use a wire brush to clean up all of the grooves in each of the pulleys to remove oil and dirt. This will help establish a good grip with the new belt during installation.
  7. Thread the new belt around the pulley system exactly as you drew it out in your diagram. Follow the diagram precisely, making sure the correct side of the belt touches the correct pulley - the ribbed side should touch a ribbed pulley.
  8. When you get to the last pulley, pull the tensioner arm with one hand so that the belt is slack while you wrap it onto the last pulley.
  9. Start the car, and allow it to idle for a few minutes. Then check that the tensioner arm position is between the two high/low marks on the tensioner body. If it isn't, use a torque wrench to adjust the belt tightness so that it is correct.

Slow and Careful

There are many repairs that you can learn, such as how to put a serpentine belt on a car. If you make sure that you have the right tools and carefully step through the process, you can save a lot of money by repairing your own car.

How to Put a Serpentine Belt on a Car