Car is whistling. What are the causes?

Sometimes drivers are facing an annoying and akward situation when, after starting the car, a whistling noise is heard especially when the engine is cold.

In most cases, the whistling noise coming from the car is caused by a worn serpentine belt also known as the accessory belt or ancillary drive belt. Other causes are a low amount of grease in individual bearings or rollers of the power unit elements and a bad water pump, and in rare cases, an accumulation of dirt in the car alternator.

The serpentine belt or ancillary drive belt is the most common cause of why the car is whistling. It sometimes whistles for a short time and then goes away. The reason is the presence of moisture on the belt. The sound is usually heard when driving in a puddle and the serpentine belt gets wet.

 Also, the serpentine belt can accumulate moisture when the car is parked for a long time in very high humidity conditions, such as near a car wash. You don’t need to worry about this issue because this does not a problem, as soon as the belt gets dry, the sound goes away.

Like moisture, certain car liquids can come in contact with the serpentine belt such as the coolant, engine oil, or brake fluid. In these cases, the duration of the whistling sound depends on how much liquid has come in contact with the serpentine belt.

If a large amount of these liquids is on the belt, it is better to change it because it will lose its working properties.

A loose serpentine belt tension

The belt’s synchronous operation with a pulley is ensured only by sufficient tension. When the corresponding force is weakened, the alternator pulley rotates at a certain angular velocity, but the belt on it slips and “does not keep up” with it. 

This creates friction between the inner surface of the belt and the outer surface of the pulley, which often results in whistling sounds. With a weak tension, the whistle sound can occur not only when the engine is started, but also when the engine speed rises sharply.

A worn-out serpentine belt

Like in the case of the timing belt or timing chain, the serpentine belt also needs a change. It’s not a regular change, so you should check it after about 70.000 km (43.500 miles). Over time, its rubber becomes tanned, and the belt itself loses its elasticity.

So, especially in cold temperatures, when the rubber hardens you will hear a whistle after you start the engine but it often disappears when the engine warms up.

Dirt in the streams of the alternator pulley

Also, a whistling car is caused by the accumulation of dirt in the streams of the alternator pulley. This often makes the serpentine belt to slip on its working surface, making whistling sounds.

Thick alternator bearing shaft grease

In rare cases, the whistling sound from the engine is caused by a thick grease, especially in cold weather. As soon as you start the car, the serpentine belt may slip, since the engine needs to apply more force to untwist the alternator shaft. Usually, after the lubricant gains a fluid consistency, the whistling sounds, and the belt slippage, disappear.

A worn-out tensioner roller

If the car has a tensioner roller then this part might be the reason why you hear whistle sounds from the car especially if the engine is cold. The whistle can be heard at certain engine speeds.

Checking the roller should start with checking the tension. Often, the roller starts to whistle when the timing belt is not stretched enough or Vice versa. You should know that tightening the belt too much is harmful to the individual roller bearings and pulleys that connect the specified belt.

A bad or failing water pump

Specifically, a thick bearing grease from the water pump can cause whistle sounds from the engine, especially when you start a cold engine, and the whistling goes away after the engine warms, but also the whistling can last even after the engine has the correct working temperature if there is no lubrication in the water pump bearing.

Other causes

The whistle might appear because of a failing alternator bearings, air conditioning elements. Therefore, it is also necessary to check those bearings.

Tips to eliminate the whistling sound from the engine

There are some quick ways to deal with a whistling car.

  • Tighten the serpentine belt if it’s loose;
  • Replace the water pump, roller, bearing;
  • Replace the serpentine belt;
  • Clean the streams of the alternator pulley.

In conclusion, since the most common reason why the car is whistling is due to a worn-out serpentine belt, you should start by checking it and checking its tensioner roller. Replace those two parts if need be.

When checking the serpentine belt, you need to pay attention to the presence of cracks on its inner surface when the belt bends. If there are cracks, the belt must be replaced. Please note that the belt tension also affects the life of a belt, so take that into account.

If the belt tension is loosened, it must be tightened. This is usually done using the appropriate roller or adjusting bolt, depending on the car design and its engine. If the tensioning mechanism is not provided, then it is necessary to replace the stretched belt with a new one.

When tightening an old or tensioning a new serpentine belt, you do not need to set a very high force, otherwise, the load on the generator bearing and the tension roller will increase, which can lead them to fail quickly.

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