What Does a Serpentine Belt Do?

The serpentine belt is one of those vehicle parts that many drivers pay little attention to. Designed for efficiency and durability, this belt typically retains its functionality for many years. The serpentine belt plays a crucial role in transmitting engine power to critical components such as the air conditioning compressor, power steering pump, and alternator. Over time, however, your belt can become damaged due to wear and tear.  When the serpentine belt is worn or damaged, it can cause a loss of power to the engine.

What is a serpentine belt?

A serpentine belt is a long, flexible rubber belt that wraps around various pulleys. The serpentine belt, or accessory belt, is the main belt on your engine that you see when the hood is open. It has distinctive ribs that run the length of one side, making it very easy to identify. These ribs play a crucial role in the belt's operation, providing a good grip when moving the accessory pulleys.

The serpentine belt is a continuous belt used in automotive engines to drive various peripheral accessories such as the air pump, air conditioning compressor, power steering pump and alternator. It's also known as a fan belt or accessory belt.

From the crankshaft pulley, the serpentine belt turns around other pulleys attached to various devices, including the air pump, A/C compressor, power steering pump, and alternator. The crankshaft pulley takes power from the engine and turns the serpentine belt. When this belt is fed by the crankshaft pulley, it begins to rotate and drives other pulleys.

The serpentine belt eliminates the need for multiple belts and simplifies maintenance by allowing the engine to efficiently power all accessories simultaneously.

In supercharged vehicles, the serpentine belt also transmits power to the supercharger. What's more, on many vehicles, the belt helps provide additional power for other functions, such as battery charging.

Symptoms of a Bad Serpentine Belt

A bad serpentine belt is not the kind of maintenance you want to put off. A broken belt can leave you stranded. If the alternator pulley stops spinning, there's no way to charge the battery.

There are many signs that a serpentine belt is beginning to wear out. Here are some of the most common symptoms of a worn serpentine belt.

1. No air conditioning

A defective serpentine belt robs the air conditioner of its function. If you turn on your air conditioner and find that it is not blowing fresh air out of the vents, this could be due to a defective serpentine belt.

Since this belt also drives the A/C compressor, you may mistakenly assume that there's a problem with the AC power, when in fact the problem is with the belt.

2. Squealing noises

If the front end of your vehicle makes squealing noises, your serpentine belt may be misaligned or slipping. Sometimes a simple realignment or proper tensioning of your drive belt can solve the problem.

3. No power steering

The power steering system functions properly because of the serpentine belt. Power steering allows drivers to steer their vehicles smoothly without using too much force.

Heavy steering is one of the obvious symptoms of a bad serpentine belt. Without it, steering becomes difficult and requires considerable effort.

4. Snapping or rubbing noise

If your serpentine belt is loose or frayed, you may hear a rhythmic snapping or rubbing sound in the engine compartment. This sound is often associated with each revolution of the engine. As you accelerate to increase engine speed, this rhythmic sound should increase. Sometimes it will get louder.

5. Visible cracks in the belt

The serpentine belt is easily accessible on most cars. If you want to know if your belt is defective, simply open the hood and inspect the belt yourself. If you notice visible cracks or damage anywhere on the belt, it means the belt is defective and must be replaced immediately.

6. Dead Battery

If you're driving one day and suddenly lose power, check under the hood to see if your serpentine belt is still attached. Even if you manage to start the car, a broken belt won't allow the alternator to charge the battery.

If the belt is too loose to grip the alternator pulley, you may experience a symptom similar to a broken belt.

7. Pulley Whine

If you notice an engine whine that changes with engine speed, you may want to have the serpentine belt tension checked. An over-tensioned belt puts excessive stress on the bearings of each accessory pulley and can often cause premature failure of these components.

8. Engine Overheating

For engines where the serpentine belt drives the water pump, this is the most important symptom. If the belt is damaged or worn, it can slip or break, preventing the water pump from working properly.

If the water pump is not working, coolant is not circulating through the engine, and the engine can quickly overheat. Overheating can damage engine components such as the cylinder head, head gasket, and engine block, which can be costly to repair or replace.

9. Black Exhaust Smoke

Under certain circumstances, serpentine belt failure may cause black smoke to be emitted from your vehicle's exhaust. This usually occurs when the belt is loose or broken, causing the engine to overheat.

How long will a serpentine belt last?

Serpentine belt life depends on a number of factors, including driving conditions, belt quality and vehicle model. On average, a Serpentine belt will last between 5 and 7 years, or between 60,000 and 100,000 miles. However, if your belts are exposed to excessive chemicals, temperatures or other harsh conditions, they may need to be replaced sooner than expected.