How to Guides

Serpentine Belt

Zaki Moulvi posted this on Jun 16, 2014

The serpentine belt drives peripheral devices from the rotation of your engine’s drive shaft. It is one continuous belt that often runs alternators, water pumps, compressors for air conditioning systems and other accessories when the engine is running.

Serpentine Belt History

Most automotive engines after 1980 have been fitted with a serpentine belt, however, early automotive systems required separate v-belts to run each accessory, resulting in complicated systems prone to multiple failures and requiring a lot of extra engine compartment space. As more and more systems were added that required engine-driven peripherals, it became far more efficient to combine the drive mechanisms using one, more complex, serpentine belt.

Troubleshooting and Repair

While the complete failure of a serpentine belt will result in many separate systems shutting down at once, such a catastrophic failure is rare without ample visual and auditory warning, and most belts will provide over 100,000 miles of service. A failing belt will usually fray and cause very obvious squeaking long before it finally breaks completely. As such, a visual inspection should be a regular part of vehicle maintenance, coinciding with scheduled oil changes. Many installations will preclude a simple inspection without the removal of other engine or body parts, but with the use of a mirror and a flashlight, it should be possible to judge the condition without removing the belt from the engine.

Inspect the belt for cracks, frayed edges, or missing ribs. Brittle, dry, and cracked rubber is a sign that the belt is past its useful life and should be replaced.

A squeaking serpentine belt can sometimes indicate improper tension, however most modern vehicles have spring loaded tensioning springs that keep the belt properly adjusted automatically, taking the guesswork out of this element of the installation. A properly adjusted belt will deflect less than one inch when pressed with your finger. Squeaking can also indicate misaligned pulleys or other problems with the accessories being powered by the serpentine belt. If a visual inspection shows no problems with the belt, suspect one of these peripherals as the culprit.

Provided that access to your serpentine belt is relatively straightforward, replacement is something easily undertaken by the home mechanic. The first and most important step is to carefully study the routing of the belt, as it will likely follow a complex path through all of the various pulleys it drives. In many cases the smooth backside of the belt will be used to drive some motors. Draw a diagram or take a photograph of the belt before beginning. If the belt has failed and you are unsure of its route, there will be a routing diagram in your owner’s manual.

To remove an old belt, you must first loosen the belt tensioner. The tensioning arm setup will vary from car to car, but most require a simple socket and ratchet to loosen and tighten.

With the belt loose it can be slid off the engine. Taking care to follow the proper routing path and ensuring that the belt’s grooves are properly seated on each pulley, it is then merely a matter of re-tensioning the system.

The serpentine belt system allows manufacturers to power multiple peripheral systems off the engine’s drive shaft with one continuous belt. Not only is this much simpler than previous multi-belt systems, it allows for more compact engine compartments and simpler inspection and maintenance for the home mechanic.

Categories: Autowiki Car Systems