%20(1)/1.png){kind=small}
The serpentine belt (also called the auxiliary drive belt or multi-V belt) powers the alternator, power steering pump, and on many engines the A/C compressor and water pump. When it fails, you lose charging, steering assist, and sometimes cooling—and the car may not be drivable. On Volkswagen and Audi, belt and tensioner wear are common causes of noise and breakdowns if ignored.
This guide covers the main signs of serpentine belt wear, when to replace it (and the tensioner), and why using the correct parts matters.
What the Serpentine Belt Does
A single, long belt typically runs around:
- Crankshaft pulley (drive).
- Alternator (charging).
- Power steering pump (steering assist).
- A/C compressor (climate).
- Water pump (on some layouts).
It’s kept under tension by an automatic tensioner (spring or hydraulic). If the belt slips, stretches, or breaks, the systems it drives stop working. A failing tensioner can cause slip, noise, or premature belt wear.
4 Warning Signs the Belt (or Tensioner) Needs Attention
1. Squealing or Squeaking When Starting or Under Load
What you hear: A short squeal when the engine starts, or a squeal when you turn the steering wheel at low speed or when the A/C kicks in.
Why it happens: The belt is slipping on one or more pulleys—often due to wear, glazing, oil contamination, or a weak tensioner that no longer keeps the belt tight.
Action: Have the belt and tensioner checked. If the belt is glazed, contaminated, or old, replace it. If the tensioner is weak or noisy, replace it at the same time so the new belt doesn’t fail early.
2. Cracks, Fraying, or Glazing on the Belt
What you see: When you inspect the belt (engine off, key out):
- Cracks on the inner (ribbed) or outer side, especially between the ribs.
- Frayed edges or missing chunks.
- Glossy, glazed surface where the belt contacts the pulleys (slipping wear).
Why it matters: Cracks and fraying mean the belt is past its service life and can snap without much warning. Glazing suggests slip and often points to tensioner or pulley issues.
Action: Replace the belt (and tensioner if recommended or faulty). Don’t wait for a break—failure at speed can wrap the belt around the crank and cause serious damage on some engines.
3. Squeaking or Rumbling from the Tensioner or Pulleys
What you hear: A rattle, rumble, or squeak from the front of the engine that changes with engine speed. It may be more noticeable at idle.
Why it happens: Worn tensioner bearing, idler bearing, or other pulley bearing. A failing bearing can also make the belt run off-centre and wear faster.
Action: Identify the noisy pulley (stethoscope or removing the belt and spinning pulleys by hand). Replace the faulty tensioner or idler; if the belt is old or damaged, replace it as well.
4. Battery Warning Light or Loss of Power Steering / A/C
What you notice: Charging warning light, heavy steering, or A/C not cooling. If the belt has broken, all belt-driven systems stop at once.
Why it happens: Broken or thrown belt—no drive to alternator, power steering pump, or compressor. Sometimes the belt is still there but so loose that it doesn’t turn the pulleys.
Action: If the belt is broken or missing, don’t run the engine (on some cars the water pump is belt-driven; running without it can overheat the engine). Fit a new belt (and tensioner if needed) before driving again.
When to Replace: Intervals and “Replace With”
Intervals
- Time: Many OEMs suggest inspection at each service and replacement every 5–10 years.
- Mileage: Often 90,000–150,000 km, but check your VW/Audi service schedule—some specify earlier.
- Condition: If you see cracks, fraying, or glazing, replace regardless of mileage or age.
Belt and tensioner together
- Tensioners wear (bearing and spring/damper). Replacing the belt but not a worn tensioner can lead to early belt failure and noise.
- Best practice: if the belt is due or failed, inspect the tensioner and idlers; replace the tensioner (and any bad idlers) when fitting the new belt so the system is reliable for the next interval.
Choosing the Right Parts
- Length and ribs: The belt must match the routing and number of ribs for your engine. Wrong length or profile causes slip or premature failure.
- Tensioner: Must be the correct part for your engine code; wrong tensioner can give wrong belt tension and damage the new belt.
- Quality: OEM or quality aftermarket belts and tensioners last longer and run quieter than unknown brands.
Use your VIN or engine code when ordering so you get the right belt and tensioner for your model and year.
Summary
- Squealing, cracks, fraying, or glazing mean the belt (and possibly the tensioner) should be replaced soon.
- Noisy or weak tensioner or idler bearings should be replaced when you change the belt.
- Follow the service schedule for replacement interval, but always replace earlier if condition is poor.
- Use the correct serpentine belt and tensioner for your engine so charging, power steering, A/C, and cooling stay reliable and you avoid a roadside failure or engine damage.