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Diagnosing Noise from the Serpentine Belt

Diagnosing Noise from the Serpentine Belt

A squeaky serpentine belt can be embarrassingly loud. It can also give you an advance warning of future engine problems. This WheelZine article tells you more about the diagnosis of serpentine belt noise.
Akshay Chavan
Did You Know?
Serpentine belts have been known to last for 100,000 miles, while their predecessor, the V-belt, could barely last for around 50,000 miles.
A serpentine belt is a single rubber belt fitted in modern cars, that drives all the accessories like the alternator, water pump, hydraulic steering, and A/C compressor. It is a wide rubber belt that transfers the power of the engine, to various pulleys, which, in turn, drive these accessories. In contrast, vehicles made till a few years back had individual V-belts for each appliance, such as one for the alternator, another for the power steering, and so on.
While it represents a technological advancement over its predecessor, the serpentine belt has its own share of problems, which is important, considering that it is a single belt driving a range of systems. Moreover, its failure can completely stall the engine, as it drives the water pump, which is critical for engine cooling. However, the belt displays several symptoms before it actually fails, such as distinctive sounds. Let us understand the diagnosis of noise emanating from a serpentine belt.
Causes
  • Malfunctioning pulley systems which are misaligned have a wheel out of line, or bent wheels, cannot effectively grip the belt, leading to noise.
  • A high-pitched squeal or screeching noise is heard when a loose serpentine belt slips on a pulley, further increasing friction.
  • An old and worn-out belt may emit noise because its hard and glazed surface increases friction. Moreover, a part of its outer cover may peel off and make a clicking noise as the belt moves.
  • A damaged tensioner or idler pulley, which is responsible for keeping the belt under proper tension, may get damaged, thus leading to low tension and noise.
  • Moisture may cause a loose belt to slip even more, leading to increased noise when it is raining or cold outside.
  • Damaged bearings in a pulley will push it out of place, leading to a chirping noise, along with damaging the belt.
  • Misalignment in accessories when they are replaced leads to a situation where they are farther than, or closer to the engine, than is necessary.
  • Impurities like oil, antifreeze, or grease, may cause slippage of the belt. In other cases, a pebble may be stuck in the belt or pulley, leading to a clinking noise.
Diagnosis
Observe Performance
A squealing noise heard when starting the engine, turning, or accelerating, is most probably due to a loose or worn-out serpentine belt, rather than damaged pulleys or tensioner system.

Spray Water
  1. Turn on the engine, and open the car hood.
  2. Using an atomizer, spray some water on the inner, ribbed portion of the belt, just before it leads into a pulley.
  3. If the noise recedes momentarily, and then returns, then the culprit is a misaligned pulley (mostly idler or tensioner pulley), or a worn-out pulley or belt surface.
  4. On the other hand, if the noise increases on spraying, then this indicates that the belt lacks sufficient tension, or is worn-out.
  5. If spraying water has no effect on the noise, then this can indicate either a damaged accessory component, worn-out outer surface of the belt, or that the belt is not faulty at all.
  6. To check if the outer surface of the belt is worn-out, spray water on it. Any change, or elimination of the noise indicates that the worn-out belt needs replacement.
Remove Belt
  1. To check if the belt is faulty, remove it and turn on the engine.
  2. If the sound is eliminated, then this clearly indicates that the problem lies with the belt, which should be replaced.
  3. If the sound is still heard, then there may be a fault with the driven accessories.
Check Belt Tightness
  1. Open the hood of the vehicle, and lightly press down on the serpentine belt.
  2. Ideally, it should be pushed down to ¾ of an inch.
  3. Observe the belt for any visible signs of damage.
  4. If the belt appears unworn, and sufficiently tight, then the noise is most likely due to the worn bearings of a pulley.
Reverse the Belt
  1. One way to diagnose whether a misaligned pulley is responsible for a squeaky serpentine belt, is to remove the belt and fix it in such a way that it moves in a reverse manner.
  2. If this momentarily eliminates or reduces the noise, then a misalignment in the pulley is the root cause, as reversing the belt changes its orientation towards the pulley.
  3. If this does not work, then misalignment is not the cause of the noise.
Check Pulleys
  1. Open the hood of the car and remove the serpentine belt.
  2. Slowly turn the pulley of each accessory by hand, paying attention to any sounds that may arise.
  3. Any grinding noise indicates that the bearings of the pulley are worn out.
  4. This can be confirmed by fixing the belt, and marking the edge of the pulley with a piece of chalk.
  5. Then run the engine, and if the appearance of the mark coincides with the belt noise, then this indicates a damaged bearing.
Belt Dressing or Soap
  1. After turning on the engine, spray a little belt dressing using the straw given with the bottle, for a better aim.
  2. Ensure that only a little solution is sprayed on the inside of the belt, to ensure that this doesn't make the engine messy.
  3. Alternatively, hold a bar of soap against the ribbed surface as the belt moves.
  4. If this takes care of the noise problem, even for a short while, then slippage of the belt is responsible for the noise.
  5. This step is not recommended as a long-term solution though, as it can damage the belt even further, and does not address the root cause of the problem.
Solution
  • The only way to solve the problem of a noisy serpentine belt is to replace it.
  • If the root cause is a damaged or misaligned pulley, then it should be replaced or corrected as well.
  • Since the tensioner system is designed to last as long as the belt, both should be replaced together.
  • Moreover, since a damaged belt polishes any pulleys it drives, these should be rubbed with a wire brush to make their surfaces rough, before a new belt is installed.
To prevent such problems, auto experts advise that an annual checkup of the serpentine belt, or a checkup with each oil change be carried out, to spot any issues at the earliest. Moreover, a serpentine belt should be replaced every 50,000 to 60,000 miles, or 5 years, whichever is earlier.