When a drive belt should be replaced in your car

Your engine has a number of mechanical accessories attached to it, such as an alternator, water pump, power steering pump and an air conditioner compressor. A drive belt is the part that drives all these accessories. The belt itself is driven by a pulley attached to the engine crankshaft. Most cars have one or two drive belts. When a car has only one drive belt, it might be called a serpentine belt.

Serpentine belt

This BMW engine has one serpentine belt

Drive belts

This Mazda has two drive belts

A drive belt is made of a durable rubber-based material.  In most cars, a drive belt is replaced between 40,000 and 70,000 miles, however, we have seen cases where a drive belt lasted over 100k miles. What makes the belt wear sooner? Water, road dirt, excessive heat and oil leaks can cause the belt to deteriorate prematurely. For example, if the protective shield underneath the engine (engine undercover) is broken, the belt will wear out sooner. Oil leaks can also damage the drive belt. Eventually, a worn drive belt will break.

Drive belt damaged by oil leak

Drive belt damaged by oil leak

Failed drive belt

Failed drive belt

If the drive belt breaks, your car won’t be driveable. This is because the engine will overheat if the water pump is not running. Also, if your car has a hydraulic power steering, you will lose the steering assist, as the power steering pump will be disabled. In addition, the alternator will stop supplying electric power that is needed to recharge the battery and run the vehicle electric systems.

When should the serpentine belt be replaced? Most car manufacturers don’t specify the exact mileage, but recommend to have the belt inspected during your regular maintenance visits. How can you tell if the serpentine belt needs replacement?

Worn drive belt

Worn drive belt

Worn serpentine belt

Drive belt showing cracks and missing chunks

Typically, your mechanic will look for cuts, cracks, missing chunks and other signs of wear; usually it’s fairly easy to see. For example, the belt in the first photo shows minor cracks; in the second photo, you can see cracks and missing chunks of the grooves on the ribbed side. The belt may also need to be replaced if it makes chirping or squeaking noises or if it’s stretched. It is also a good idea to replace an old drive belt when an alternator or any other component driven by the drive belt is replaced, or when you prepare your car for a long road trip.

To work properly, a drive belt must be under proper tension. Most newer cars have an automatic spring-loaded or hydraulic belt tensioner that doesn’t need to be adjusted. In older cars, the belt tension had to be adjusted manually in regular intervals. One of the symptoms of a loose drive belt is a loud squealing or screeching noise that lasts for a few seconds after the engine is started. Often, drive belts are replaced as a kit with the new tensioner and other hardware.

Replacing the serpentine belt may cost from $75 to $250, depending on the car.
Is it easy to replace the serpentine belt as a DIY project? If you have sufficient mechanical skills, proper tools and the belt routing diagram, it’s not very difficult. Your parts store may help you with the routing diagram and tools.
by TA Editors. Photo credits: Testing Autos
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