Older vehicles had V-belts that ran one or two accessories. Depending on the accessories, your vehicle might have had from one to four V-belts. In newer vehicles, one long belt runs every accessory. These belts are called serpentine drive belts. Instead of keeping tension on the belt by adjusting the tensioning screw in a bracket, the serpentine belt uses a spring-loaded tensioner. Chances are, you’ll replace the serpentine belt at least once before you have to replace a tensioner. In most cases, you’ll replace the belt several times before the tensioner. But every time you replace the belt, you should check the tensioner. A bad tensioner could ruin a brand new belt.

Symptoms of a Broken Tensioner

The tensioner is located on the outside of a serpentine belt which is the smooth side of the belt. It puts tension on the belt to keep it tight. The serpentine belt stretches over time, so the tensioner puts more tension on it to keep it tight. A broken tensioner might click or squeal. It could also break a belt, in which case, you’d hear the belt slapping if it gets hung up in one of the pulleys. Additional symptoms of a broken belt or tensioner include:

  • The battery won’t charge and the battery light comes on.
  • The car starts to overheat.
  • You lose power steering.
  • The air conditioner won’t work.

Checking the Tensioner

Every time you replace the serpentine belt, check the tensioner. Spin the pulley to see if it spins freely. If you hear grinding or the pulley doesn’t spin freely, replace the tensioner.

When you replace the belt, it should take a lot of muscle power to move the tensioner. If you can move it easily, the spring tension is most likely not tight enough.

You can also check the tensioner by checking belt tension. If you can twist the belt more than 90 degrees, the belt is stretched beyond the tensioning capabilities of the tensioner, or the tensioner is not doing its job. Finally, if you notice sporadic issues, such as the power steering skipping, the vehicle not constantly charging, or the air conditioning not working all of the time, you might check the tensioner.

Tensioner Problems

A serpentine belt tensioner can wear out over time, or it could have other problems. The following are what you should look for when checking the tensioner.

  • Look for rust in the tensioner housing. Rust will eventually cause the tensioner to freeze.
  • Clean any dirt or mud out of the tensioner.
  • Bad bushings cause noise—usually grinding noises—but can also cause the belt to vibrate.
  • If the pivot arm is loose, it could make the belt track wrong and destroy the belt.
  • If the spring is weak, it won’t put enough tension on the belt.
  • If the tensioner housing has cracks or other damage, it could break the belt and destroy other parts in front of it, including the radiator.

Replacing the Tensioner

If your vehicle does not have a belt routing diagram, take a picture of the belt before taking it off or make a sketch of the routing. Using a tensioner release tool, loosen the tension on the belt. If you are not replacing the belt, you can try to leave it on most of the other pulleys. Remove the bolts holding the tensioner onto the block. Remove the tensioner. Replace the old tensioner with the new one and secure the belt back into place.