When does the timing belt need to be replaced?

The timing belt is the most important belt in the engine. It's a toothed belt that runs the engine camshaft(s). It's called a timing belt because it precisely "times" the up-and-down movement of the pistons with opening of the valves.
Timing Belt Timing belt. See more illustrations: Fig 1. Fig 2.
A timing belt replacement is one of the high-price maintenance items many motorists have to deal with.

Why does a timing belt need to be replaced? Over time, it wears out. 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, a timing belt stretches. Symptoms of a stretched timing belt include lack of power and slow pick-up. In some cars, a stretched timing belt can also produce a dull rattling noise coming from the timing belt area.

When does a timing belt need to be replaced? In most cars, the recommended timing belt replacement intervals vary between 60,000 and 106,000 miles. In some modern cars, the intervals are even longer. First, you need to know what engine does your car have? The same car could have different engines. One way is to decode your car's VIN number.
For example, AutoZone provides a VIN decoder that will tell you the engine size. Another way is to check the Vehicle Emissions Label that is typically located under the hood. For example, according to this label that is attached to the inner side of the hood, this 2019 Volkswagen Jetta has a 1.4L engine. This engine does have a timing belt. Once you know the engine size, you can find the timing belt replacement interval in the maintenance schedule.
Timing Belt Timing Belt. Ford F-150 3.0L V6 Power Stroke Diesel
It is posted in the Maintenance section of the owner's manual or in a separate brochure.

Can a timing belt last past the recommended interval? Yes, in some cases. We came across a number of 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 changed. "I'll just keep checking the belt condition; it still looks OK" – was the owner's response.

On the other hand, there are many cases when a timing belt breaks prematurely. How can you tell if the belt is in good shape or needs to be replaced as soon as possible? Can a timing belt condition be inspected? Yes. A timing belt is covered by plastic or metal covers. Your mechanic can remove one of the covers and visually check the timing belt condition. For example, this timing belt in the photo belongs to the Acura TL with 52,000 miles.
Timing Belt condition This timing belt is still in good shape. Acura TL.
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 the inspection, the mechanic found that the timing belt shows cracks. The owner rightfully decided to have it replaced. See another photo of a worn-out timing belt.

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 a 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. In a non-interference engine, there is still some clearance between fully open valves and a piston in the top position.

How to know if your engine is an interference engine? Here is the link to Timing Belt Replacement Interval Guide, courtesy of the Gates Corporation. In this guide, the interference engines are marked with the star sign.
Timing Belt Timing belt synchronizes the rotation of the crankshaft and camshaft.
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. 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. A 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. A timing chain is a maintenance-free unit and rarely needs replacement. Read more: When a timing chain needs to be replaced.

How to know if a car has a timing chain or belt? First, you can 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.
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 the tools and the skills, it's not that difficult. In a small 4-cylinder engine, for example, in Toyota Tercel, it can be done within two hours. The hard part is usually the removal of the harmonic balancer (main engine pulley) as the bolt holding it is very tight and sometimes you might need a special puller to take the pulley out. Another difficult task is to set the timing properly and adjust the belt tension when the new belt is installed. For this you might need the factory service manual.