What is an auxiliary / serpentine drive belt?

Auxiliary drive belt image

The auxiliary drive belt is also known as the serpentine belt, and runs all the auxiliary systems on the front of the motor. It shouldn't be confused with the timing belt which serves a completely different purpose.

The belt runs through a system of pulleys and turns the alternator, water pump, air conditioning compressor, and sometimes the power steering pump and the cooling fan, and is driven by the engine's crankshaft.

Old cars typically used two or three v-shaped belts to connect everything, but this took up more room than a single belt system, and caused more parasitic loses from friction.

The serpentine belt's wide, flat, multi-ribbed design can power several different components and takes up less space. With careful engineering, accessories can be turned with the back of the belt with less friction for better fuel economy.

When to change your drive belt

“Drive belts are designed to last for between 50,000 miles and 100,000 miles”

Haynes recommends that you look over the auxiliary drive belt every time you change the oil. If this serpentine belt fails it typically isn't catastrophic, but your car will quickly overheat after a few miles without the water pump turning. You should plan on changing the belt every five years or 60,000 miles even if it looks okay. Replacements are inexpensive and typically require only a few minutes to change.

Find info on checking the belt here - Checking the Drive Belt

All cars are slightly different, so if it is time to change your drive belt, use our before you begin checklist, and find your car for specific instructions.

Warning

Look for signs of fluid contamination from oil or coolant leaks which will quickly ruin a newly installed belt.
Find Your Car

Every car is different, so find yours for make/model specific instructions...

How to change your drive belt

This sample video contains general instructions. Find the full step-by-step task for your model

A very brief summary of the task:

  1. Disconnect the negative cable from the battery.
  2. On front wheel drive cars, you may need to remove the passenger side wheel and inner fender for access
  3. If your car has a spring tensioner, rotate it to release the belt tension. Be careful not to let it spring back suddenly
  4. On manually adjusted belts, loosen the adjuster until the belt has enough slack to be removed
  5. Make note of the path of the belt around the pulleys
  6. Remove the belt from the pulleys
  7. Locate the new one on the pulleys, making sure it is properly aligned
  8. If manually adjusted, set the tension according to the Haynes manual
  9. Replace the wheel liner and wheel
  10. Reconnect the battery

Why you should change your drive belt

The drive belt is key to the operation of a car’s ancillary items, such as cooling and charging. If the belt fails, the engine will quickly overheat from the water pump not being turned. Your first sign of a failed auxiliary drive belt will likely be the warning light for the charging system coming on to indicate the alternator is not turning. You should still be able to drive for a few minutes to safety.

When a drive belt fails it tends to do so in one go, snapping and getting spat off. Sometimes the belt splits longitudinally and long strands will slap the hood. You may not realize the belt is failing, but as soon as you notice it is important to replace the belt before it can cause any damage.

Before you begin

Tools you will need

Only basic tools are required for this job, although you may need to raise the car to remove the splash shield or the wheel and inner fender.

  • Floor jack and jack stands
  • Ratchet and socket set
  • Torque wrench
  • Breaker bar
  • Ruler

Parts you may need

  • Replacement belt
  • Tensioner (if needed)