Serpentine Belt Tensioner

Changing a Serpentine Belt Video

A serpentine belt tensioner is designed to automatically hold a predetermined amount of tension on a drive belt while the engine is in operation. If the drive belt is loose, the tensioner has failed or the wrong size belt has been installed. The tensioner should be about half way through its travel to hold proper tension, most have a gauge stamped on them to determine belt stretch for replacement. On rare occasions an engine can buck or jerk at start up and can suddenly cause a belt to jump out of place. Other problems can occur if the drive belt snaps, this can be due to fatigue of the belt. The most common reason for the belt to snap is age coupled with the natural wear and tear of the belt. Before belt tensioners there was a simple adjustment bolt that was used to set the tension on the belt. The disadvantage to this set up is once the belt stretches slightly it would have to be re-adjusted. If re-adjustment is not performed the belt can create a loud screeching noise. A belt tensioner consists of a main body, swing arm, tension spring, pulley and pulley bearing.

Drive Belt Tensioner
Drive Belt Tensioner (appearance will vary)

The drive belt or serpentine belt is an essential component of your vehicle. The primary belt function is to supply power to the steering system, water pump, air pump (if equipped) air conditioner and alternator. This belt is connected to the drive pulley of the engine to supply power. If the belt fails it will almost always render your vehicle inoperable until the drive belt is replaced. Typically most people are able to replace a serpentine belt themselves with basic automotive tools. When replacing the belt draw a diagram of the belt routing before you start to avoid confusion. If you have removed the drive belt and need the belt routing you can look it up on a belt routing diagram.

Serpentine Belt
Typical Serpentine Belt

There are two different types of belts primarily; the first is a serpentine belt which tends to cross the motor several times to operate additional components. There are several names that are used to describe a serpentine belt, including Poly-V, Multi-Rib, and even a Micro-V Belt. However, all of these terms mean the exact same thing and do not change the way the belt is routed, or the type of material the belt is constructed from. A serpentine belt tends to have several V's in the belt that act as better grip for the drive pulley and components of the drive belt system.

Replacing your car's serpentine belt is a relatively simple repair that can be done in a few minutes with minor tools in most cases. Always wear protective gloves and eyewear before you begin.


For regular maintenance lift the hood and do a complete visual inspection of the belt tensioner. Be sure there is no lateral movement or slow spring action. If it appears that any of these conditions exist replace the tensioner with a new unit. Replacing the tensioner before it fails is always advisable; it will prevent you from breaking down on the roadside. The drive belt is generally a component that requires maintenance. If you notice that you have to continuously change serpentine belts, you should have all of your pulleys examined for excess debris lodged inside the pulley groves. This condition will cause the tensioner to wear out prematurely. 

 If further technical assistance is needed, ask our team of certified car repair technicians.

Related Car Repair Information


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


Please use our question form if you have a specific question about your car as we are not able to give you a full answer on this page.

Article first published (Updated 2013-08-19)