Serpentine Belt vs. Timing Belt: Understanding Their Roles and Differences in Your Car

While your engine's crankshaft drives both belts, the timing belt and the serpentine belt are not the same thing and serve very different functions in your vehicle.

The serpentine belt drives the vehicle's accessories like the AC, alternator, and power steering pump. In contrast, the timing belt connects the camshaft(s) to the crankshaft to synchronize the engine valves and the pistons.

Both timing belts and serpentine belts are critical to the proper operation of a vehicle's engine.

Timing Belt vs Serpentine Belt: Purpose

What Does A Serpentine Belt Do?

The serpentine belt is a rubber belt that drives the engine accessories (parts external to the engine) of the vehicle. These include the following:

1. alternator
2. power steering pump
3. AC compressor
4. water pump (sometimes)
5. acts as a fan belt for the cooling fan (sometimes)
6. auxiliary air pump (sometimes)

What Do Timing Belts Do?

The timing belt gets its name because its primary function is to maintain the exact timing of the engine's valves in the engine's combustion chamber.

Timing belts accomplish this function by driving the car's internal components. These include the following:

1. camshaft(s)
2. water pump (sometimes)
3. oil pump (sometimes)
4. injector pump (sometimes in diesel applications)

Read our in-depth post on timing belts here.

Timing Belt vs Serpentine Belt: Location

Where Is The Serpentine Belt Located?

The serpentine belt gets its name from how it is woven around the various pulleys of the car's accessories, much like a serpent or a snake.

Your vehicle's serpentine belt is located outside of the engine and, in most cases, can be accessed and inspected quickly and easily.

Where Are Timing Belts Located?

Timing belts are located under the timing cover and are challenging to access.

Depending on your vehicle's engine configuration, you must remove the alternator, a wheel, the fan, or an engine mount to access the timing belt and service it properly.

You can usually inspect a timing belt through the inspection port in the timing cover; it is sometimes difficult to gauge its condition.

Serpentine Belt vs Timing Belt: Construction

What Are Serpentine Belts Made Of?

A serpentine belt is a friction drive belt, so it is made of a rubber compound that stretches around the accessory pulleys and drives them purely by friction.

The serpentine belt is a V-belt with grooves cut into it longitudinally that match up with grooves in the pulleys.

These grooves create a greater surface area for contact.

Unlike the timing belt, some slippage by the serpentine belt can occur, although it will squeal or whine if the belt is worn out or loose.

What Are Timing Belts Made Of?

The timing belt is a direct drive belt with cogs, aka gears, built into the belt that matches up with the gears of the crankshaft pulley and the camshaft pulley.

It is constructed stiffer than the serpentine belt and is made not to stretch and withstand extreme heat and, to some degree, possible oil or coolant contamination.

Serpentine Belt vs Timing Belt: Failure

What Happens If A Serpentine Belt Breaks

If you suspect a failing serpentine belt, you must book an appointment to have it looked at by a mechanic or replace the belt yourself if you are capable.

If a serpentine belt failure occurs, the car's accessories will no longer work.

First off, your car's alternator will no longer charge your vehicle's battery, and the battery will quickly drain.

A car's battery drains extremely fast, and you probably won't get further than a couple of blocks before your car dies and won't start.

The car will also lose power steering, making it extremely difficult to steer.

The serpentine belt may also drive your water pump or your car's cooling fan.

If either of these isn't functioning correctly, your car will quickly overheat, which again could be catastrophic and costly with a complex repair required with an expensive charge for both parts and labor.

What Happens If A Timing Belt Breaks

You should safely park your vehicle and shut your engine off immediately if you suspect a failing timing belt.

If timing belt failure occurs, the engine's pistons won't be properly synchronized with the engine's intake and exhaust valves.

Timing belt failure could be either a slipping belt or if a belt breaks completely.

This could allow internal contact between the pistons and valves, depending on whether your vehicle has an interference or non-interference engine.

When timing belts are damaged, they are susceptible to breaking

If contact occurs, costly repairs will be needed with an expensive bill for parts and labor.

Timing chains are often preferred over timing belts because it can be somewhat challenging to know if you have a bad timing belt.

Failure Prevention

Due to the critical nature of both the serpentine belt and the timing belt, you must follow your vehicle's recommended preventative maintenance schedule to save you much future money and headaches.

Replacement Costs

There is a drastic difference between the cost of replacing a serpentine belt versus a timing belt.

Both the timing belt and serpentine belt have recommended replacement intervals.

The make and model of the vehicle determines the timing belt replacement cost. Click to see our timing belt replacement cost analysis on different makes and models.

Replacement Costs For A Serpentine Belt

The belt replacement interval for a serpentine belt is generally between whichever comes first, 7 to 9 years or 90,000 miles. But, again, check with your mechanic or owner's manual for the interval for your specific vehicle.

Replacing a serpentine belt is usually a straightforward process.

A capable mechanic can complete the job quickly, and the belt is inexpensive.

Due to low labor and parts costs, most serpentine belt changes come out to not more than 100 dollars.

Replacement Costs For A Timing Belt

The replacement interval for a timing belt is generally between whichever comes first, 5 to 7 years, or between 60,000 to 105,000 miles. Again, check with your mechanic or owner's manual for the interval for your specific vehicle.

Replacing a timing belt is quite costly, mainly because it is labor-intensive.

Most timing belt jobs take over 5 hours to complete.

The timing belt is not very expensive, usually only around 50 dollars. Still, because it takes a lot of labor time to remove the components necessary to change the belt, it is highly recommended to change out other parts made accessible while you're at it.

These include the following:

1. water pump
2. timing belt tensioner pulley
3. idler pulley
4. related gaskets and seals

Generally, the timing belt is available in a timing belt kit that includes the belt and the water pump, pulleys, gaskets, etc., for around 100 to 300 dollars.

Add in labor time, and timing belt jobs can cost between $800 to 1500 dollars for parts and labor at a shop.

There is a huge difference in difficulty between changing a serpentine belt and a timing belt, although neither requires you to take your vehicle to a mechanic.

Can I Change A Serpentine Belt Myself?

Even for a novice, a serpentine belt change is relatively easy on most vehicles.

The proper tools required for the job are common and inexpensive, and the vehicle won't need to be put on jacks.

There are videos available on Youtube on almost every make and model of vehicle.

That said, a bad serpentine belt should be dealt with immediately, so if you can't or don't have time, you should have the serpentine belt replaced by a mechanic.

Can I Change A Timing Belt Myself?

A timing belt is quite complex and requires tools, such as a timing belt pulley puller, that most novice mechanics do not have.

The job will take much longer for a beginner than it will for an experienced mechanic, and there is the possibility that the installation will be done improperly, which could lead to engine damage.

A timing belt change is possible even for a beginner if proper procedures are followed.

It's best to give yourself a few days so that parts or tools can be bought if you find you need them.

As with serpentine belt changes, there are timing belt change videos available on Youtube for virtually all makes and models of vehicles.

In Conclusion

Timing belts and serpentine belts are not the same and serve different but critical purposes.

If you're unsure or think either belt needs to be changed, it is essential to consult a mechanic as failures can lead to engine damage.

If you're unsure if your vehicle has a timing belt or a timing chain, look for your model at the timing belt resources at this link.