Your Complete Idler Pulley Buying Guide

March 20, 2025

5 min read

March 20, 2025

5 min read

Your serpentine belt drives a lot of different pulleys. It could drive your air-conditioner compressor, power steering, alternator, and your water pump. The idler pulley ensures that the serpentine or drive belt follows the right path. A different part, the belt tensioner, puts tension on the belt while the idler pulley guides it along. Learn about what an idler pulley does and when to replace it - opens in new window or tab..

Even though it’s an important part, replacing an idler pulley is a simple task. See our complete how-to guide and video for replacing your idler pulley - opens in new window or tab.. The job should take less than one hour.

Buy the Correct Type of Idler Pulley

A grooved Dayco 89009 idler pulley, displayed on a white background. — This grooved idler pulley fits a wide range of vehicles.

An idler pulley is a wheel-shaped pulley on a shaft. The serpentine or drive belt runs along that pulley and stays in tension.

Automotive pulleys are usually made from steel or a glass-filled polymer (plastic). Look for designs with sealed lifetime bearings and dust covers that avoid dirt and other debris causing premature wear.

There is some variation between idler pulleys because they are designed to match different belts. The idler pulley should match the corresponding belt. Here are the main types of idler pulleys:

Flat: Flat idler pulleys have a flat, smooth surface which the belt travels along. Use this type when the pulley needs to sit against the flat part of the belt. Some flat idler pulleys have a flange (or lip) to help keep the belt on the pulley.

Grooved: A grooved idler pulley has distinct ridges that match the belt to help ensure the belt does not slip off the pulley. If you have a grooved pulley, the number of grooves should match the existing belt. Grooved idler pulleys might also have a flange, a protruding rim.

How to Find an Idler Pulley That Fits Your Vehicle

A mechanic in overalls, wearing black nitrile gloves, holds two idler pulleys. The pulley on the left is connected to its tensioner. — It's essential to find the right idler pulley for your vehicle's make and model.

Fit and compatibility are essential when buying a new idler pulley. A repair manual for your vehicle should have the necessary specifications. We also recommend using the eBay Parts Finder - opens in new window or tab.. Enter your vehicle’s year, make, model, engine, and trim to get a list of compatible pulleys. Two vehicles from the same year with different engines may not share the same idler pulley.

The inner and outer diameters and the width of the replacement pulley should match the existing pulley. If possible, use a micrometer— a precision tool that measures in small increments—to verify the dimensions.

Steel pulleys are commonly used in heavy duty applications, but are subject to corrosion.

What does it cost to buy a new idler pulley?

In most cases, a new pulley costs between $50 and $100. The price depends on the materials used and the type of vehicle. The price is also influenced by whether the pulley is grooved or flat and the quality of the bearings.

We recommend investing in the highest quality pulley because many other components—including the alternator, water pump, and power steering—depend on the belt to function correctly. Popular brands include Dayco, Gates, and Timken.

Related Parts and Accessories

A grooved serpentine belt, displayed on a white background. — This robust grooved serpentine belt is designed for use with General Motors pickup trucks and vans.

Belt tensioner: The idler pulley ensures that the tension is correct on the belt, but it’s the belt tensioner - opens in new window or tab. that applies the pressure to keep it there. While you have the belt off the car, we recommend replacing the tensioner.
Idler pulley mounting bolts: If your idler pulley is deteriorated, the chances are good that the mounting bolts have also rusted or weakened over the years. Inspect them. You may need replacement idler pulley mounting bolts.
Serpentine belt: While you are replacing the idler pulley, we recommend replacing the serpentine belt - opens in new window or tab.. As the pulley wears out, the belt can get damaged.

Consider an Idler Pulley Kit

A 1999-2008 manual Porsche 911 Idler pulley and serpentine belt kit, displayed on a white background. — This kit includes three idler pulleys, along with the serpentine belt and required hardware.

If you are having problems with your idler pulley, there may be other parts that need attention. You might be able to bundle all the needed replacement items together in a kit. Replacing all the related parts at one time saves time, money, and effort.

Idler pulley and belt kit: If you are replacing the pulley and the belt, a kit combines these two compatible components in a single package.

Idler pulley and belt tensioner kit: If you are pulling the belt assembly apart, an idler pulley and belt tensioner sold in a kit can be helpful. A kit often includes everything you need to overhaul the belt system and put it in top working condition.

About the author

Michael O'Connor

Michael O’Connor is a Bay Area writer who grew up restoring classic cars. These days, he works on his 1979 Fiat Spider. Michael is an alum of Sonoma State’s Creative Writing program. He began professional auto writing in 2015, contributing to AutoList, CarGurus, Endurance Warranty, Safe-Guard, and other car sites.

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This article is meant to provide general guidance only. Automotive maintenance, repair, upgrade, and installation may depend on vehicle-specifics such as make and model. Always consult your owner's manual, repair guide for specific information for your particular vehicle and consider a licensed auto-care professional's help as well, particularly for advance repairs.