Serpentine Belt – Function – Failure Symptoms – Easy Replacement

Serpentine Belt - Function - Failure Symptoms - Easy Replacement
Serpentine Belt - Function - Failure Symptoms - Easy Replacement

The serpentine belt, is probably the most commonly used belt today.

The belt snakes its way, through multiple accessories, the crank pulley, an idler pulley or two, and a tensioner.

This one long belt runs, every engine-driven accessory, including the water pump, alternator, a/c compressor and power steering pump.

The serpentine belt, has greatly simplified, the operation of under-hood pumps and pulleys. Sooner or later, it will need replacement. Because, it is, a wear item.

Serpentine Belt, Function

So, modern vehicles (usually) just have one belt, that winds through multiple pulleys, to power all the accessories.

Basic Belt Routing
Basic Belt Routing

While using just one belt, is the most efficient and reliable option; it also means that when your car’s serpentine belt breaks, everything stops working! You’ll lose power steering, the A/C will quit, your battery will eventually die, and the engine might overheat. Plus, it could also, damage the engine accessories it controls.

Serpentine Belt, Inspection

With so many systems counting on it, it’s important to periodically inspect it. The nice thing about this belt is, you can see it ! Unlike a timing belt, that is covered up and needs, a lot more labor to inspect. Consequently, it needs to be checked for signs of, fraying, cracking, or glazing. As a general rule, recommended replacement is, every 30,000 to 60,000 miles.

Signs of, fraying, cracking, or glazing.
Signs of, fraying, cracking, or glazing.

Serpentine Belt, Failure Signs

Usually, a serpentine belt, lasts a long time. But eventually, the heat and friction, will wear it down and it will need replacement.

Here are some signs of a failing serpentine belt:

  • Signs of wear (cracking, glazing, fraying, etc.)
  • Squealing or chirping sound (indicates a slipping belt)
  • Performance loss (power steering failure, sudden car battery drain or stalled engine)
  • Check Engine Light
  • Unusual noises
  • Engine Overheating

Serpentine Belt, Easy Replacement

You should be, able to easily replace this belt, in under an hour. You should only need basic hand tools. Also, some people feel more comfortable, have a repair manual, but it is not required.

Things to do, before you start your project:

  • Today, everyone has a mobile phone. Take pics of your belt routing, the way and directions the belt flows.
  • The serpentine belt routing diagram is usually located on a tag in the engine compartment.
  • We should have serpentine belt routing information here on our site as well.
  • Don’t forget to get the new Serpentine Belt !

A Belt Tension Tool Is Also Handy, They are Everywhere.

Belt Tension Tool
Belt Tension Tool

The Tear Down Process

  • Firstly, look at the way the old belt wraps around all the pulleys.
  • Next, look for and locate the self-adjusting belt tensioner.
  • The back side of the belt runs against the tensioner. So, it will appear, more like a smooth roller, than a pulley.
  • Position the wrench or special removal tool on the tensioner. Make sure you have room, to remove the tool, once the tensioner is released.
  • You’ll notice that the tensioner tool, is a flat bar rather than a ratchet. Consequently, this will help you get into the tight clearance for the tensioner’s roller. NOTE, there are, hydraulic belt tensioners as well. Discussed in, up coming Blog Posts.
  • Always be careful, when releasing tension from the belt. Be prepared to feel some force, as you release the tension.
  • Finally, remove the old serpentine belt.

Check all pump and idler pulleys.
Check all pump and idler pulleys.

Inspection Process

  • Check the tensioner pulley for wear, by using your hand to spin it before installing the new belt.
  • Noisy, loose or overly tight tensioner pulleys, will need replacement.
  • Also, check all pumps and idler pulleys, to make sure they move freely too.
  • Check the idler pulleys and the pulleys for the; water pump, alternator, smog pump, A/C compressor and any other accessories, for wobble or deflection.

Assembly Process

  • Install the new serpentine belt. Line up all belt ribs, in the pulley grooves.
  • And, be sure that the belt, is not twisted. Finally, tighten the tensioner.
Belt installation
Belt installation

Make sure the belt tension is correct:

  • If the belt tension is too low, the belt will slip causing noise, extremely high temperatures and premature belt wear.
  • As a result, can lead to the, poor functioning, of the belt-driven accessories. ( poor charging and steering issues )
  • If the tension is too high, this will cause, excessive wear, to the belt-driven accessories. ( pulleys and seals )

Do another visual inspection and double-check the belt and tensioner, for correct tightness, before starting your engine.


If your serpentine belt wears out, becomes damaged or contaminated, or breaks; engine accessories will not be able to spin at the proper speed. As a result, leading to decreased power to the electrical system. This can lead to a sudden lost of power assist for the steering system. As a result, leading to the steering wheel all-of-a-sudden, becoming very hard to turn.

A broken serpentine belt may stop the water pump from circulating coolant through the cooling system. Consequently, causing the engine can overheat. And it may stop the alternator from generating power to operate the vehicle’s electric/electronic systems and recharge the battery. Finally, the headlights will dim, the radio will not work, and the battery will die.

Thank You !