What is Serpentine Belt? – When Should You Replace It?

What is the Serpentine belt?

A serpentine belt is a single, continuous belt used to drive multiple peripheral devices in an automotive engine, such as an alternator, power steering pump, water pump, air conditioning compressor, air pump, etc.

The belt may also be guided by an idler pulley and/or a belt tensioner (which may be spring-loaded, hydraulic, or manual).

To allow the belt to pass over more than three pulleys with a large enough wrap angle to avoid slipping, idler pulleys which press against the back of the belt are included, forcing the belt into a serpentine shape.

To accommodate this bidirectional flexing while remaining strong enough to transfer the total force required by multiple loads, serpentine belts are almost always of multi-groove (multi-vee, poly-v, or multi-rib) construction.

Serpentine Belt vs. Timing Belt

Don’t get confused a serpentine belt is not the same thing as a timing belt. The serpentine belt and timing belt have very different functions in your vehicle.

The timing belt is located inside the engine and keeps the crankshaft and camshaft in sync. This ensures that the engine intake and exhaust valves open and close in time with the pistons so the engine runs smoothly.

The serpentine belt is what keeps the engine accessories running smoothly and efficiently. It connects the engine crankshaft on the outside of the engine to all of the engine accessories.

You can easily tell the difference between the two when you look at the grooves. A timing belt has horizontal “teeth” designed to fit the cogwheels of the crankshaft and camshaft. A serpentine belt has multiple V-shaped grooves that run vertically along with the belts.

These belts often need to be replaced around the same time, so ask your mechanic or consult the owner’s manual to see if you need to replace your timing belt too.

Didn’t cars used to have more than one belt?

Back in the day, cars had individual belts for many components. Though each belt could be replaced individually, these cars experienced inconsistent or compromised performance as individual belts began to wear down. Now that vehicles employ a single belt the serpentine belt that’s no longer an issue. That said, it’s critical that regular inspections are done to make sure the belt is in good shape.

How often does a serpentine belt need to be replaced?

Serpentine belts are built to last much longer than before because of advancements in rubber technology. Under ideal conditions, a belt should stick with you for an average of 60,000 to 100,000 miles. Pretty impressive. However, some belts are manually tensioned and may need to be adjusted.

Others have a self-tensioning mechanism that can experience wear over time and may need to be serviced. One thing to remember: in most cases, if the belt breaks, the vehicle will stop running.

How many belts do most vehicles have?

Today, there’s one belt to run them all well, for the majority of vehicles. It’s called the serpentine belt. Some rides may have an additional belt to run select accessories, but the serpentine does the bulk of the work. Before this all-in-one serpentine solution, cars were equipped with many different belts to power individual parts and components.

What happens as a belt gets older?

They can wear, fray, crack or become shiny or “glazed,” and rubber parts can peel off the belt. An aging belt can also begin slipping or squealing, become contaminated with fluid or become misaligned, in which case it will need to be replaced. An old belt can even snap, leaving you up the creek; without one, drive torque to all of the engine’s accessories is lost.

What is the benefit of having a belt replaced?

Driving on an old belt is a disaster waiting to happen because it powers most all of an engine’s accessories. That means when your belt breaks, slips, and, ultimately, wears out, everything from the power steering pump to the alternator and air conditioner stops working.

What’s more, the parts it controls can become severely damaged. Broken hoses and belts are bad; a damaged engine is even worse. By replacing your belt periodically, you can minimize the risk of breakdown.

Serpentine Belt Diagram

Serpentine Belt Diagram

Top 7 Bad Serpentine Belt Symptoms

A bad serpentine belt is not something you can just put off and wait to deal with. The entire functionality of your vehicle may be compromised when your belt is worn, damaged, cracked, or snapped.

1) No Air Conditioning

A malfunctioning air conditioner can be attributed to a lot of things. Since the serpentine belt keeps the air conditioner functional, a bad serpentine belt will take that function away from it. If you turn on your air conditioner and see that it does not blow out cool air from the air vents, this could possibly be due to a bad serpentine belt.

2) Squealing Sounds

If the front area of your vehicle makes squealing sounds, then your serpentine belts might be misaligned or slipping. Sometimes it might just take a realignment or proper tensioning of your serpentine belt to fix this problem.

In other cases, the belt is probably damaged and will need to be replaced.

3) No Power Steering

The serpentine belt allows the power steering system to function properly. Power steering is what gives drivers the ability to smoothly steer their vehicle without needing to apply too much arm strength.

If you have a bad serpentine belt, then it will be harder to move the steering wheel to steer your vehicle.

This issue could also be caused by low power steering fluid. While you’re under the hood, check to make sure the power steering reservoir has the recommended level of fluid.

4) Overheated Engine

The serpentine belt is what activates the water pump which helps cool the engine. If you have a damaged or worn serpentine belt, then it won’t be able to activate the water pump. This means that your engine will begin to overheat since it cannot be cooled down anymore.

You will see this happening as the temperature gauge on the dashboard shows the needle moving toward the red zone. Don’t let this continue for too long or else your entire engine could get damaged.

5) Visible Cracks on Belt

The serpentine belt is easy to access in most cars. If you want to know if your belt is bad, simply open the hood and look at the belt for yourself. If you notice visible cracks or damage to anywhere on the belt, this means the belt is bad and needs to be replaced right away.

6) Dead Battery

If you’re driving along one day and suddenly lose power, check under the hood to see if your serpentine belt is still attached. Even if you’re able to get the car started, a snapped serpentine belt will not allow the alternator to charge the battery.

Without the alternator’s charge, your car will eventually die from the electricity used by the spark plugs, the radio, and the headlights. A vehicle can often run without a working alternator for a bit of time, but not for long.

If the belt is too loose to maintain grip on the alternator pulley, you may experience a similar symptom as a snapped belt.

7) Pulley Whine

If you start to notice a whine from the engine that changes with engine speed, you may want to have the tension of the serpentine belt double checked. A belt that is too tight puts too much load on the bearings in each of the accessory pulleys and can often cause premature failure of those components.

One of the most common failure modes for water pumps is actually bearing failure, caused by a serpentine belt that was too tight. If you think your belt may be too tight, it’s best to address this issue as soon as possible to prevent expensive engine damage caused by overheating.

Serpentine Belt Replacement Cost

If there are strange car noises under your hood, the culprit could be a faulty serpentine belt. But what does a serpentine belt replacement cost? Of course, it depends on your make and model as well as labor costs, but in general a replacement serpentine belt costs around $70-$200 (plus taxes and fees), including around $50 for the belt and around $150 for the labor.

The ease of accessing the serpentine belts will determine how much the labor costs are. Some model vehicles have serpentine belts easily accessible, which means the labor should take under one hour. But if the belt is in a more complicated area, it could take about 2 hours.

Easy to reach belts can actually be changed at home with minimal tools. Some belts can be removed by loosening one bolt, while others have a belt tensioner you have to pull on with a wrench to give the belt some slack. You might consult a repair manual for your specific vehicle to see if you can do this yourself.

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