Timing Belt Vs. Serpentine Belt - Differences Explained

Serpentine Vs Timing Belt
Serpentine Vs Timing Belt |

By Petar Milošević - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=32175327, By Una Smith - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=2954075

While both belts are driven by your engine’s crankshaft, the timing belt and the serpentine belt are not the same thing and serve different functions in your vehicle.

Overview: Timing Belt Vs. Serpentine Belt

Timing BeltSerpentine Belt
Main PurposeSynchronizes timing between pistons and valvesDrives engine accessories such as AC, alternator, cooling fan etc.
LocationHard to get at - underneath timing coverExternally outside engine
ConstructionStiff rubber with gearsV-belt made of stretchy rubber
In Case Of FailureMotor won't run - possible catastrophic damage due to valve interference Motor will run a short time - possible catastrophic damage due to engine overheating
Failure PreventionReplace every 5 to 7 years or 60,000 to 100,000 miles (check owners manual) Replace every 7 to 9 years or 90,000 miles (check owners manual)
Replacement CostsParts: $25 to $200, Labor: $500 to $1300Parts: $15 to $30, Labor: $40 to $80
Can You Replace It Yourself (As A Novice)Yes, easily with few toolsYes but difficult with many tools

Purpose

The biggest and most important difference between a timing belt and a serpentine belt are their purposes.

What Does A Serpentine Belt Do?

Serpentine Belt
Timing Belt Diagram|

The serpentine belt’s purpose is to drive your car’s accessories (parts external to the engine). These include the:

  • alternator
  • power steering pump
  • AC compressor
  • water pump (sometimes)
  • cooling fan (sometimes)
  • auxiliary air pump (sometimes)

What Does A Timing Belt Do?

Timing Belt
Timing Belt Diagram|

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

The timing belt accomplishes this function by driving the car’s internal components. These include the:

  • camshaft(s)
  • water pump (sometimes)
  • oil pump (sometimes)
  • injector pump (sometimes in diesel applications)

Read our in-depth post on timing belts here.

Location

Where Is The Serpentine Belt Located?

The serpentine belt gets its name from the manner in which 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 Is The Timing Belt Located?

The timing belt is located under the timing cover and is difficult to get too. Depending on your vehicle's engine configuration oftentimes the alternator, a wheel, the fan,or an engine mount have to be removed to properly access the timing belt and service it.

Although the timing belt can usually be inspected to some degree through the inspection port in the timing cover it is sometimes difficult to gauge its condition.

Construction

What Is A Serpentine Belt Made Of?

A serpentine belt is a friction drive belt so it is made of a rubber compound that is made to stretch around the accessory pulleys and drive 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 is allowed to occur although if a belt is worn out or loose it will squeal or whine.

What Is A Timing Belt Made Of?

The timing belt is a direct drive belt with cogs, aka gears, built into the belt that match up with the gears of the timing belt crank 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.

Failure

What Happens If A Serpentine Belt Breaks

If a serpentine belt breaks your car's accessories will no longer work. First off your car’s alternator will no longer charge your vehicle's battery which 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 serpentine belt may also drive either your water pump or your car’s cooling fan. If either of these aren’t functioning properly your car will quickly overheat which again could be catastrophic and costly with a complex repair required with a costly charge for both parts and labor

What Happens If A Timing Belt Breaks

If a timing belt breaks your engines pistons won't be properly synchronized with the intake and exhaust valves. This could allow for contact to occur depending if your vehicle has an interference or non-interference engine. If contact occurs costly repairs will be needed with an expensive bill for both parts and labor.

Failure Prevention

Due to the critical nature of both the serpentine belt and the timing belt it is imperative that you follow your vehicle's recommended service interval to save you much future money and headache.

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.

Timing Belt Replacement Costs?? Click to see our study on different makes and models

Replacement Costs For A Serpentine Belt

The replacement interval for a serpentine belt is generally between whichever comes first, 7 to 9 years or 90,000 miles. Check with your mechanic or owners manual for the interval for your specific vehicle.

Replacing a serpentine belt is usually a very simple process. The job can be completed quickly by a capable mechanic and the belt is inexpensive. Due to both a low labor cost and a low parts cost 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. Check with your mechanic or owners manual for the interval for your specific vehicle.

Replacing a timing belt is quite costly mainly due to the fact it is labor intensive. Most timing belt jobs take over 5 hours to complete.

The timing belt itself is not very expensive, usually only around $50 dollars but 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:

  • water pump
  • belt tensioner pulley
  • idler pulley
  • related gaskets and seals

Generally the timing belt is available in a timing belt kit that includes the belt along with 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 in total for parts and labor at a shop.

Can You Do It Yourself?

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

Can I Change A Serpentine Belt Myself?

Even for a novice, a serpentine belt change is quite easy to do on most vehicles. The proper tools required for the job are common and inexpensive and the vehicle won’t need to be jacked up. There are videos available on Youtube on most every make and model.

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.

That being said 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 vehicle.

In Conclusion

The timing belt and serpentine belt are not the same thing and serve different but very important purposes. If you're unsure or think either belt needs to be changed it is important 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 look at timing belt resources here.