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We’ve all heard that the trick to quieting down engine pulley noise is rubbing a little soap or deodorant on the belt while the engine is running. Sure, it’ll lube things up and get you motoring along without feeling like that person in the drive-through, at least until you waste a perfectly good stick of Irish Spring only to find the noise persists. 

Even in the instances where life hacks like this work, they generally only mask the problem rather than actually fix anything. That’s why it’s usually best to cut right to the chase and do things the “hard” way the first time around. 

Thankfully, chattering/whining pulleys are pretty easy to sort out. And there’s a good chance that it’s a simple idler pulley that’s the source of those awful sounds. So let’s dive into how you can confirm that it is so you can get ready to make the repair. 

What Is an Idler Pulley?

An idler pulley is a simple component in the serpentine belt system. It’s not attached to any accessories, and while it may be mounted near the tensioner pulley on some applications, it’s only there to guide the serpentine belt. 

Some idler pulleys may have a ribbed surface, while others have a smooth outer section. Which is present depends on what part of the belt it comes in contact with as ribbed pulleys mate with the ribbed part of the belt and smooth go to smooth. The good thing about it being so simple is that it’s usually easier and cheaper to replace than the tensioner pulleys and those that are attached to accessories like an alternator or power steering pump. 

How Does an Idler Pulley Work?

Roller bearings are hard at work to allow your idler pulley to rotate. What’s featured inside isn’t all that different from the sealed bearings you might find inside any kind of motor or even skateboard trucks, for that matter. The thing about bearings is that, though they’re crucial to keeping main components from wearing away, they’re sacrificial. Over time, the bearings in the cage will wear, as will the races they ride on. When they do, the bearing will become sloppy and whatever they’re inside will fail to operate smoothly. 

To say that bearings are solely to thank for an idler pulley’s function is understating its function, though. As we know, the belt rides on the idler pulley, and it provides guidance that’s necessary for the belt to remain secured on the other accessories it’s driving. That means the outer portion, smooth or ribbed, is as much to thank for the function as the bearings. 

How to Tell If You Have a Bad or Failing Idler Pulley

We’ve already established that you have some kind of chatter, whining, or generally terrible sound coming from your engine. The first thing we need to do is pinpoint the source of the noise. You will want direct access to the pulleys, so get the serpentine belt out of the way. 

Locate the idler pulley and give it a visual inspection. If there’s any kind of corrosion on the exterior of the pulley, it’s a good indication that the internals aren’t doing so hot. You can clean it up for good measure, but you’ll likely need to replace it in short order anyway. 

There are two physical tests you can perform on the pulley with the belt off. The first is to grab the pulley by the flat sides and give it a couple of shakes. If there’s excessive play, you know the bearings are shot. The next thing you can do is spin the pulley. You’re looking to make sure that it does spin some, but not for a long time. Both free spinning and a pulley that doesn’t want to rotate indicate bad bearings. 

If none of these inspections reveal an issue with the idler pulley, you’ll want to repeat it on the other pulleys in the system until you find which is the cause of your heartache. Don’t rule out the possibility that the serpentine belt may also be worn.  

How Long Does a Serpentine Belt Last?

Under normal circumstances, a serpentine belt should last 60,000 to 100,000 miles. If the idler pulley is bad, it can cause excessive wear to the belt and even destroy it. Keeping good pulleys in place is essential to the long life of the serpentine belt.

How To Prevent an Idler Pulley From Going Bad

Unfortunately, there’s not a whole lot that you can do to keep idler pulleys from going bad. They rely on bearings, which are going to wear down and need replacing at some point or another. That doesn’t mean taking care of your vehicle won’t help extend the life of your pulley, though. Keeping the engine clean and clear of excessive debris and moisture should ensure the idler pulley will live a long, healthy life. 

It is worth paying attention to the replacement parts you use, too. It’s no surprise that the more affordable options use lower-grade components that will wear away and corrode faster than others. Even if you do opt for the more premier choices, you should give the pulley a thorough inspection before tossing it on. Take a look to see if there are any signs of rust or issues with the bearings before you install it. If you can spot any problems now, you’ll want to swap it for another so you don’t have to do the job again sooner rather than later. 

The Questionnaire

Car Bibles answers all your burning questions. 

Q. Can you drive without an idler pulley?

A. No, you can’t drive without an idler pulley. The engine will run and even move the car some. However, some vital accessories are dependent on the serpentine belt, including the alternator and water pump. Without these parts at work, you’ll drain the battery and overheat the engine. 

Q. Can you replace an idler pulley at home by yourself?

A. As long as you have the right tools, you can do the job on your own. Replacing the idler pulley is usually as simple as removing the serpentine belt, unbolting the old pulley from the front of the engine, and installing the new one.

Q. Could a bad idler pulley damage a serpentine belt?

A. Yes, a bad idler pulley can wreak havoc on the serpentine belt. Corrosion on the surface and drag from bad bearings can be very hard on the belt and may even cause it to dislodge under extreme circumstances. 

Q. How much does it cost to replace an idler pulley? 

A. That depends on the cost of a new pulley for your car and if you intend to do the work yourself. The new pulley can cost anywhere between $50-$100. Taking it to a shop will tack on labor costs which can drive the overall price to around $200. 

Learn More About Idler Pulleys From This Helpful Video

Car Bibles understands that many of you aren’t text-based learners, preferring a kinesthetic approach. We got your back and pulled a video from one of our trusted sources to help you understand what an idler pulley does and how it works. 

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