When does the timing belt need to be replaced?

For most cars, recommended timing belt replacement intervals vary between 60,000 and 106,000 miles. In some modern cars, the intervals are even longer. Some car makers also list the time interval (e.g. every 7 years). First, you need to find out your car's engine size, because many cars offer several engine options. Knowing the engine size, you can find the timing belt replacement interval in the maintenance schedule.
Timing Belt Timing belt. See more illustrations: Fig 1. Fig 2.
It is posted in the Maintenance section of the owner's manual for your car or in a separate Warranty and Maintenance brochure.

What is a timing belt and why should it be replaced? The timing belt is the most important belt in the engine. It's a toothed belt that runs the engine camshaft(s); see the animation below. It's called a timing belt because it precisely "times" the up-and-down movement of the pistons with the opening of the valves.

Why does the timing belt need to be replaced? Over time, it wears out, see the photo. If the timing belt breaks, the engine will stop running and will need repairs. The repair cost will depend on the damage. If the vehicle has an interference engine, the repair might be expensive, read more below. Another reason is that over time, the timing belt stretches. Symptoms of a stretched timing belt include a lack of power, slow pick-up and the Check Engine light coming on. In some cars, a stretched timing belt can also produce a dull rattling noise coming from the timing belt area.
How to find out your car's engine size? One way is to decode your car's VIN number that you can find on the factory VIN sticker or in the left lower portion of the windshield. The VIN number of your vehicle is also printed on your vehicle's insurance paper or vehicle title. VIN Decoders:
AutoZone
NHTSA
Another way is to check the Vehicle Emissions Label that is typically located under the hood.
Screenshot of the owner's manual Download the owner's manual and search for 'timing belt'. This is the OM for the 2019 Ford Escape.
For example, this label lists the engine size of this 2019 Volkswagen Jetta as 1.4L engine. This engine does have a timing belt.

Once you know the engine size, check the owner's manual. You can even do it right from your phone. Download the pdf owner's manual for your car and search for 'timing' or 'timing belt' or 'maintenance schedule'. Check out this article: Where to download the owner's manual for your car. See this screenshot: we downloaded the owner's manual for the 2019 Ford Escape and searched for "timing belt." As you can see, it only mentions the 1.5L engine; the other two engines available in this vehicle don't have a timing belt.

Can a timing belt last past the recommended interval? Yes, in some cases.
Timing Belt Timing Belt. Ford F-150 3.0L V6 Power Stroke Diesel
We came across several high-mileage cars with a timing belt that has never been changed. In fact, as we worked on this article, we discussed the Toyota Highlander belonging to one of our colleagues. It had almost 200K miles and the timing belt has never been replaced. "I'll just keep checking the belt condition; it still looks OK" – was the owner's response.

On the other hand, there are many reports of a timing belt breaking prematurely. How can you tell if the timing belt is in good shape or does it need to be replaced as soon as possible?

Can the condition of the timing belt be inspected? Yes. The timing belt is protected by plastic or metal covers. Your mechanic can remove one of the covers and visually check the timing belt condition.
Timing Belt condition This timing belt is still in good shape. Acura TL.
For example, this timing belt in the photo belongs to the Acura TL with 52,000 miles. The owner wanted to check the timing belt condition before a long trip. According to the mechanic, this belt is in good shape and can last for a while longer.

The timing belt in the photo below belongs to the Honda Civic with 150,000 miles. The engine was still running fine, but upon inspection, the mechanic found that the timing belt showed cracks. The owner rightfully decided to have it replaced.

What happens if a timing belt breaks? There are two types of engines: an interference and non-interference.
Worn timing belt Worn out timing belt. Honda Civic.
In an interference engine, if the timing belt breaks while driving, there is a good chance that the engine might be severely damaged. A non-interference engine will stall if a timing belt breaks, but further damage might be limited. The difference is that in an interference engine, valves that are fully open will be hit by the piston as it travels to its top position. Read more and see the animations: Interference versus Non-interference engines.

The timing belt replacement in a 4-cylinder engine costs from $250 to $650, plus extra if a water pump or other parts are replaced.
Timing Belt AnimationTiming belt animation. Timing belt synchronizes the rotation of the crankshaft and camshaft.
In a V6 or V8 engine, the price to replace a timing belt ranges from $450 for just a belt to over $1,000 if a water pump and related hardware need changing.

Is it necessary to replace a water pump, timing belt tensioner and other hardware when doing the belt? It's not necessary, but is usually recommended, because it requires a little extra labor. In some cars, a hydraulic timing belt tensioner is known to leak and fail at higher mileage. The water pump also wears out over time, read more: When does the water pump need to be replaced?

Do all cars have a timing belt? No, many modern cars have a timing chain instead. The timing chain is a maintenance-free unit and rarely needs a replacement. Read more: When a timing chain needs to be replaced. How do you know if the car has a timing chain or belt? Check your maintenance schedule or call your dealer. Another option is to ask your mechanic during your next oil change. Toyota published the list of models that have a timing belt online: Does my vehicle have a timing belt or timing chain?. The Gates Timing Belt Replacement Interval Guide we mentioned before has a list of cars that have a timing belt.
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Of course, you can always google: '2017 Honda Accord V6 timing belt or chain?'

Is it difficult to replace a timing belt as a DIY project? If you have technical skills, tools and the factory service manual with all the instructions, it can be done. In some cars it's fairly easy, in others it takes a lot of work. In a small car with a 4-cylinder engine such as an older Honda Civic, for example, it can be done within two hours. In a car with a transversely-mounted V6 engine, space between the frame and the engine is limited. The hard part is usually to remove the harmonic balancer (main engine pulley) as the bolt that holds it is very tight. You might need a special puller to take the pulley out. The same bolt will also need to be torqued properly after the new belt is installed. Another difficult task is to set the timing correctly and adjust the timing belt tension.