How to Diagnose a Loose or Stuck Belt Tensioner on Your Car or Truck

Hey, friends. It's Len here from 1A Auto. Today, I want to talk to you about belt tensioners. Let's talk about where they are, what they do, and some symptoms of when they go bad.

Firstly, when we're talking about serpentine belt tensioners, I want to let you know what they are. A serpentine belt tensioner is something that applies a regulated amount of pressure to that serpentine belt so it can spin all those pulleys as needed.

Some vehicles, there's going to be things in the way that makes it hard to see. So, we'll just get those out of the way so we have a better look. Potentially it's going to be located in different areas depending on the vehicle. Some vehicles, once you pop the hood, you're gonna see your engine might run front to back or even transversely, which means that it would go side to side. Assuming it's front to back like this one, I would look right down along the front and that's right where you're going to see the belts. We can see some of the major components that the belt rides along.

You have your alternator. Everybody knows what these are. You're gonna have your idler pulley, which pretty much just spins around in a circle and it doesn't really do too much of anything. Generally, you'll have a power steering pump, assuming you have a hydraulic pump. You're also gonna have a water pump, you're going to have a crankshaft and you should have a tensioner.

Now, different types of vehicles have different types of tensioners. In all honesty, some vehicles don't even have a tensioner at all, but we'll get into that in a second. Overall, the three types of tensioners that you're more than likely going to find on your vehicle's engine would be something like this, which is spring loaded. You might also find one that's hydraulic, and then of course you'll have the type that's adjustable and you would have to manually do that. It's not self-adjusting.

Now to determine where your spring-loaded tensioner is, it's not always the easiest to just go ahead and try to look fort. Sometimes people have a hard time knowing exactly what it looks like. So, I would just look at my belt system. I would find an area that has a long distance between one pulley and the next. This is a pretty good spot right here. And then I would just give it a nice tug.

When you tug on this, you should notice that the belt comes out a little bit and if the belt comes out, then that means that the tensioner is functioning. So just look around as you pull to see which one of those parts might be moving. Whichever part is pivoting is the belt tensioner.

Now, before we go too much further, it's important to remember that not all belt tensioners are spring-loaded tensioners. Some tensioners actually have a little bolt that you would adjust the tension that way. So, if you gave the belt a tug, you're not really going to see any movement from your belt tensioner.

Now, just to reiterate on what your belt tensioner actually does is it's supposed to apply a specific amount of pressure to your serpentine belt as it runs across all of your pulleys. By pulleys, I mean things such as, maybe, your alternator. You also have an idler pulley generally. More than likely, you're going to have a power steering pump pulley especially if you have a hydraulic system.

More than likely, you're going to have a water pump that needs to run off of it as well. Not all vehicles have a water pump that runs off of the surf belt. Some of them actually run right with the timing belt, which is completely different.

Now some of the symptoms of a failing self-adjusting tensioner could be something slight as maybe you hear a little bit of a chirp coming from your serpentine belt or even a squeal, especially if it's wet outside. The reasons for that could either be because, maybe, your serpentine belt is in poor condition, maybe it's cracked or something like that. But assuming your serpentine belt is in good condition, more than likely, it probably comes down to the tensioner itself.

If the tensioner isn't functioning as it should, and maybe it's holding too much tension on that belt going across all the pulleys, you're probably gonna notice some bearing noise coming from things such as maybe your alternator, your power steering pump, or even the idler pulley.

Also, if the self-adjusting tensioner isn't actually holding enough tension to the belt, you might notice some sort of squealing noise, especially if it's moist outside. You might also notice that, maybe, your alternator isn't charging properly and you could probably even pop your hood and take a look at it. And you might see your belt just kind of shaking around because it doesn't have the proper amount of tension.

A simple way to test to see if your self-adjusting tensioner is working or not is to simply go ahead and grab onto the belt and give it a nice tug. If you don't see the tensioner moving, then you know that it's probably frozen. If you see the tensioner moving when you pull on this, but it doesn't actually fully retract to the point where it puts proper amount of tension on your belt, it could also be bad in that way.

So theoretically, the tensioner could either be frozen to the point that it's not moving at all, or it could be so weak that it's not putting enough pressure on this.

Now, if you find that you have a tensioner issue with your vehicle, maybe it's putting too much tension or maybe even not enough, it's something that you're more than likely going to want to get fixed ASAP. If your serpentine belt tensioner is putting too much pressure on any of those pulleys, whether it's your alternator, your power steering, your water pump, any of those pulleys are gonna have bearings inside.

If the belt's pulling too hard on those pulleys, it's gonna put extra pressure on those bearings, in which case it's going to cause damage overall. Now it's important to remember that not all vehicles have only one belt. Some vehicles will have multiple. In this case, we have an extra belt that goes to the AC compressor. That belt, of course, needs a tensioner, unless you have just a stretch belt assembly, some vehicles have that, but if you see this unit right here, that's actually a tensioner unit itself as well.

To test this, you can use a 3/8 drive ratchet, as you can see, and then try to pry down on it and see if it moves. A lot of times, these AC ones will freeze up. It goes down and it, kind of, comes up, but it doesn't put very much tension. That could be an issue.

Now, if you're checking your belt tensioners and you happen to notice that it's bad, whether it's frozen or maybe it's just too weak, more than likely there's going to be damage that's been done to your serpentine belt as well. The next thing you would need to do is, of course, inspect that serpentine belt and make sure that it's in good condition.

What I mean by that is go ahead and remove it if it's easy enough for you to take off, take a peek at that ribbed area which is gonna be the groups that run across the pulleys and look to see if they look like they're cracked or maybe if they're just, kind of, like super deep. Because the serpentine belt groups should really only be about this deep to where my fingers are, but if it keeps getting worn to the point where it's this deep, it's gonna cause an issue.

So, we try to make an educational video for you on checking out your belt tensioner. Let me just ask you a question real quick. Does it make much sense to replace only the tensioner and not replace the belt? Well, I'm going to leave that up to you, but me personally, I'm taking the belt off the majority of the way anyway. Especially since I like to remove it fully to check it, I might as well just go ahead and replace it because more than likely if the tensioner is damaged, it's probably caused some damage to the belt as well.

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