How To Tell Which Pulley Is Squealing?

Any odd noise coming from the engine bay can be unnerving, and squealing or squeaking sounds are no different. Still, there is no immediate cause for worry because replacing a pulley is fairly cheap in most cases; plus, they can hardly cause much trouble even if they seize. But of course, have the problem fixed as soon as you can because waiting to be stranded by the side of the road is never a good idea.

Before we go into more detail, here is how to tell which pulley is squealing. The first method is to buy a mechanic’s stethoscope and probe each pulley with the engine running. Next, you can do the same thing with a screwdriver, but you can also try with a big funnel or a hose. And last and best option is to remove the belt and check all pulleys for side-to-side play and spinning resistance.

bad idler pulley symptoms

What Causes Pulley To Squeal

Pulleys are pretty simple components and are essentially just ball bearings with a belt groove on the outer side. So, the only thing that can fail in a pulley is the bearing, which, when it fails, will start making intermittent squealing noises. The same thing will happen if the bearing has side-to-side play causing it to vibrate, or if the factory lubrication has drained or become insufficient.

Also, when a pulley begins to fail, either the bearings will make a squealing noise or the belt. The belt makes noise because it’s sliding over the failing pulley that now has rolling resistance or because the pulley is moving side to side, again causing the belt to slip. That’s why it’s a good idea to inspect the belt when the time comes to replace the pulley.

How To Tell Which Pulley Is Squealing

Here we will go into more detail about every method on how to tell which pulley is squealing, explaining why some methods are better than others so you can pick the best one for your circumstances. Also, keep in mind that some methods can be dangerous, so read about each one carefully.


Using a stethoscope is probably the most professional way how to tell which pulley is bad. Plus, the mechanic stethoscopes aren’t that expensive either, and you can find them on Amazon for around ten bucks and probably cheaper in your local hardware store.

The way this method works is that you put the stethoscope in your ears and put the other end, the probe, on the center of each pulley. The pulley center is the bolt holding it down, and it’s not spinning.

However, be careful not to tangle the stethoscope in the belt or poke the probe into the spinning pulley. And from there, it’s pretty simple, once you probe the right pulley, you will hear the squealing clear as day without it being drowned out by engine noise. The whole process won’t take longer than 5 minutes unless you have to remove some plastic covers.


Using the screwdriver as a stethoscope is one of the oldest mechanic tricks. For this method to work, you need a long screwdriver with a hard plastic handle or, better yet, a metal tip on top of the handle. Then, lean the screwdriver head on the center of each pulley, and put the handle top in your ear. Also, make sure to cover your other ear because the noise won’t be as clear or as loud as it would be with a real stethoscope.

However, keep in mind that this method is by far the most dangerous on this list. Regardless of how long the screwdriver is, it won’t be long enough to keep your hands out of the engine bay. Also, the screwdriver will slip much easier, which can cause it to pull your hands into the belt or kick back into your ear and possibly knock you out.

So, don’t do this method unless you absolutely have to, and keep in mind that it’s usually reserved for stationary components like the valve cover (listening to valve lifters) and fuel injectors.


Although it may not sound effective right off the bat, a lot of mechanics use hoses and funnels to find a squealing pulley. That said, you do need a large diameter hose, like two inches, for example, or a really big funnel. But if you have access to either of the two, they are much safer than using a screwdriver.

That’s because you don’t need to lean the hose or funnel against the pulley; instead, just bring one end of the hose near it with the engine running and listen to squeals on the other end. And if you are using a funnel, put the narrow side near the pulley. Also, it’s a good idea to cover your other ear, but it should be pretty easy to hear which pulley is squealing.

Remove the Belt

In case you want to replace the pulley right away and don’t need the car to get new parts, removing the belt to check which pulley is squealing is the best method on this list. That way, you will know for certain which pulley is faulty, plus you will discover if any other pulley is failing but hasn’t started squealing yet. And lastly, you will know if the belt is good or needs to be replaced.

Now, removing the belt is different for every car, so we can’t say how easy it will be for you, but in most cases, it doesn’t take longer than 20 minutes. Once you remove the belt, spin every pulley by hand, and if you notice spinning resistance in any of them, they are faulty.

And the same goes if you see the pulley whirring or shaking. And lastly, check if the pulleys have a side-to-side play; in other words, if they seem loose. If the answer is positive, it means the pulley bearing is faulty; however, a small amount of play can be normal, say one millimeter or less.

squeaky pulley when cold

What To Do If Pulley Is Squealing

If your pulley is squealing, the only thing you should do, and the only thing we can recommend, is that you replace it. If the pulley is squealing, it means it’s just a matter of time before it seizes and possibly breaks something else along the way, not to mention you will be left stranded.

Unfortunately, it’s hard to tell how much it will cost you to replace a pulley. For example, replacing the idler pulley rarely costs more than $80 with parts and labor included, while replacing the alternator bearings rarely costs less than $150.

That said, most alternators have integrated bearings into the pulley, so let’s not worry about that too much. Instead, the best thing we can say is that from what we have seen on YourMechanic, the average cost to replace a pulley is $120, with parts and labor included.

How Do You Stop a Pulley From Squeaking

The best way and the only correct way how to stop a squeaky pulley is to replace it. However, if you want to stop it from squeaking until you replace it, you can spray some WD40 on its bearings. However, with WD40, the pulley will only stop squeaking for about 10 miles or so, if that.

Also, WD40 is not a lubricant which means it will accelerate the pulley failure leaving you less time to replace it. Furthermore, you are risking the WD40 ending up on the belt, which will cause it to slip, leading to a whole slew of different malfunctions, from the AC not working to the alternator not charging the battery. Ultimately, there is no magic pulley squeak spray, so avoid this at all costs and get the pulley replaced as soon as you can.

How To Diagnose A Squeaking Pulley! 1ROAD YoutTube 


Q: Is it my belt or pulley squealing?

If you hear a constant and extremely loud squeal, then it’s most likely your belt squealing. However, if the squealing is intermittent and doesn’t turn everyone’s head wherever you go, then it’s one of the squealing pulleys.

Q: Why is one of my pulleys squealing?

If your pulley is squealing, then its bearing is failing. That means the pulley is misaligned, or it has spinning resistance, causing the belt to slip over it. Also, the pulley bearing may not be sufficiently lubricated because of age, in which case the bearing is squealing.

Q: What does a misaligned pulley sound like?

A misaligned pulley sounds like intermittent squealing. In other words, the squealing is constant but sporadic, making a squeak a couple of times every second, also described as chirping. That’s also one of the most common bad idler pulley symptoms.

Q: Can you spray WD40 on a squeaky pulley?

Yes, you can spray WD40 on a squeaky pulley, and nothing bad will happen immediately, but that is not recommended. WD40 is not a lubricant, plus it washes away the factory bearing grease leaving the pulley without any lubrication in a matter of 10-15 miles. That will significantly shorten the lifespan of any pulley, let alone a squeaky one that’s already on its last legs.

Q: Is a squeaky pulley bad?

Yes, a squeaky pulley is bad. Squeaking is a dead giveaway that the pulley bearing is failing and that it’s already making spinning resistance or is misaligned. Replacing such a pulley as soon as you can is in your best interest.

Q: Is it safe to drive if a pulley is squealing?

Yes, it’s safe to drive if a pulley is squealing; however, it’s not recommended. It’s only a matter of time before a squealing pulley seizes and possibly leaves you without power steering and battery charging. In both cases, you will have to call a tow truck, plus losing power steering while driving can be dangerous in some circumstances.

Final Words

Of the four different ways to check which pulley is squealing, removing the belt and spinning each pulley by hand is the best method. After all, you will end up having to replace whichever pulley is faulty anyway. But if that’s not an option, the second best choice is to use a mechanic’s stethoscope, which is the most bulletproof way of specifying which pulley is squealing.

And lastly, you can use a large hose or a big funnel, which is the preferred backyard mechanic method. And whatever you do, try to avoid using a screwdriver as a substitute for a stethoscope, but that will work too.

Ibro Cehic

Ever since I was bitten by the automotive bug during early childhood I was obsessed with cars. My first driving experience came when I was ten and I already started tinkering with cars and motorcycles at thirteen. So, right from the beginning, I knew my life would revolve around cars, even if I wasn’t sure how that would happen. And today, thanks to my second passion, writing, I get to share my love for automobiles with other enthusiasts through my articles.

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