Why Does My Serpentine Belt Keep Coming Off [7 Easy Fixes]

The most common reasons that can keep you wondering why does my serpentine belt keep coming off again and again are a malfunctioning tensioner, bad pulleys, failed bearings, oil or coolant leak, failing AC compressor, malfunctioning water pump, and faulty bushings.

why does my serpentine belt keep coming off

Keep reading this article to find out what causes the serpentine belt to keep coming off in detail and how you can fix the issues that cause this problem. You’ll also learn how to align the pulleys on the serpentine belt. Let’s start!

Why Does My Serpentine Belt Keep Coming Off [7 Easy Fixes]

We’ll discuss what can cause a serpentine belt to come off in this section. Here are the main reasons behind it:

Note: You can also read how to fix the Humming Noise when accelerating and decelerating problems.

1. Malfunctioning Tensioner

The drive belt in your car is connected to several pulleys and needs constant tension to work properly and stay in its place. If the belt is not aligned correctly to the tensioner, it can come off.


When the tensioner is out of alignment, your serpentine belt can keep popping off the pulley as it won’t have sufficient tension. You’ll often hear noise coming from the tensioner as well when it goes bad.


Tensioners are usually of two kinds – manual and automatic. If you have a manual tensioner, you can adjust it so that it puts the correct tension on your belt and keep it from coming off. But if you have an automatic tensioner, you cannot adjust it.

Replace the automatic tensioner with a new one when it goes bad is the solution in this case. It’s an easy job to replace the tensioner if you’re comfortable with car repairs. Tensioners can cost you $100-$200 if you replace them yourself.

2. Bad Pulleys

Another common reason that can leave you thinking why would a serpentine belt come off is a bad pulley. Inspecting and fixing this issue is straightforward. Take the serpentine belt out and spin the pulleys on which the belt sits.

If you hear a cranking sound coming from them, that means they have play in them and they’re causing the drive belt to keep coming off. Otherwise, the pulleys are in good condition and they’re not the ones causing the issue.


The first thing you should try when you have bad pulleys is to put grease in them. That can solve the problem in some cases and help maintain the tension to keep the serpentine belt in place. Replace them if putting grease in them doesn’t do the trick.

3. Failed Bearings

There are bearings on the inside of the pulleys that can go bad and cause the pulleys to malfunction. If your serpentine belt slipped off, failed bearings could be the reason behind it.

 failed bearings


Replace the pulley with the failed bearing as you can’t replace the bearing inside the pulley as a separate unit. Replacing the pulley will keep the drive belt in its place if failed bearings were causing the issue.

4. Oil Or Coolant Leak

If there’s any oil or coolant leak in your car, it can get to your serpentine belt. It’ll become soft, weak, and begin to wear out when that happens. The drive belt will keep on being more and more stretched.

The tensioner will not be able to compensate for that extra slack of the drive belt. It’ll become too loose and eventually come off. You can easily identify if leaking oil or coolant is causing the belt to slip off by visually inspecting it.

There’ll be oil or coolant all over the serpentine belt when any of them starts to leak. The belt itself will also feel soft due to the wear and tear it faces after coming into contact with the liquid.


This problem goes deep and you’d need to address the issue that’s causing oil or coolant leaks in your car. Determine the source of the leak first and solve that issue. There are many causes behind leaking oil or coolant in your car.

Sometimes, both of them will leak and mix with each other. Follow this guide to learn about the main reasons why coolant mixes with engine oil and how you can fix it.

Once you take care of that, you need to replace the serpentine belt as it has become worn out because of the leak. Doing that should solve your problem and you’ll no longer have to think about why my driver’s belt keeps coming off.

5. Failing AC Compressor

The pulley of the AC compressor is connected to the serpentine belt for most vehicles. When the AC compressor fails, the pulley gets locked in its position.

ac compressor pulley

It doesn’t make the necessary movement needed for the serpentine belt to maintain the tension and keep rotating.

The serpentine belt will come off in that case. So, if you still haven’t found the answer to why would a serpentine belt come off, be on the lookout for a failing AC compressor.

You’ll also see smoke coming from your engine in a few cases when it happens. That’s because the drive belt and the crankshaft pulley will be running but the compressor pulley won’t move.


If the AC compressor pulley isn’t rotating smoothly, it needs to be replaced with a new one. But to get to the root of solving the problem, you need to identify what’s causing the AC compressor to fail and fix it.

6. Malfunctioning Water Pump

If the drive belt is connected to the water pump, then a failing water pump can develop a leak and make the serpentine belt come off. But some of the water pumps are electric and they won’t cause any issues with the drive belt.

If you’re thinking why does the belt on my car keep coming off and you still haven’t found the answer, check your engine and see if the water pump is connected to the serpentine belt.

If they’re connected, inspect your water pump thoroughly as it could be causing the problem.


Oftentimes, there’ll be play in the pulleys of the water pump when they go bad. If you notice that and you can diagnose that you have a faulty water pump, you need to replace it with a new one.

7. Faulty Bushings

This cause of failure isn’t common for all cars but it happens enough for us to include it in our list. There are rubber bushings in the crankshaft pulley in many vehicles. These bushings catch the vibrations so that those vibrations aren’t transferred to the belt.


When they fail to do their job properly, the crankshaft pulley becomes wobbly and may cause the belt to come off. So, if you’re still wondering what causes the serpentine belt to keep coming off, failed bushings could be the answer you’re looking for.

Moreover, for vehicles with higher mileage, the bushings can crack and the pieces surrounding the bushings can become separated. That’ll also cause the belt to come out.


When the bushings of the pulleys go bad, replacing the bushings will do the trick. But you may not be able to find spare bushings that you can replace and it also needs a lot of expertise to replace them.

So, when you have bad bushings on any of the pulleys, you’ll most likely have to replace the entire pulley. That’ll allow you to drive your car normally again and keep your drive belt from coming off.

How To Align Pulleys On Serpentine Belt

There are many laser alignment tools available that you can use to align the misaligned pulleys on a serpentine belt. But what’s more important is to first figure out what’s causing the issue behind your serpentine belt making noise in the first place.

There’s an easy test for that. You’d need to do the test with your engine running and it’s recommended that you take safety precautions before starting the test. Keep all your clothing and tools away from the running engine to protect yourself from any injury.

First, you need to perform this test to fill a spray bottle with tap water. The next thing you need to do is to duplicate the conditions that cause your drive belt to make noise.

Identify where the noise is coming from. If you’re having difficulty locating the origin of the noise, start with the shortest belt span. That means starting with the area where there is the least distance between two pulleys. Spray the water and look out for these symptoms:

  • If the belt noise increases, that means there’s not enough tension on the belt. Both the tensioner and the belt should be replaced.
  • If the noise goes away for a while and returns, it means one or more of the pulleys in that location are misaligned. They’ll have to be aligned.
  • If there’s no change in belt noise, look for the next shortest belt span and repeat the test there.

The water acts as a lubricant and they help identify whether the issue lies with the belt or the pulleys. If your test confirms that the pulleys are misaligned, you have to realign them. You can use traditional or laser alignment tools for this job.

The traditional alignment method is often quick but not accurate. You’d need mechanical tools like tape measures, wire springs, calibrated cones, etc. But we’ll be using the laser alignment tool as you can achieve a high level of precision when using them.

The misalignment of the pulleys can be parallel, angular, or pulley run-out. Turn off the engine, remove the drive belt and make sure the electric fans of the radiators are disconnected before you start diagnosing what kind of misalignment your pulleys have.

You’d need a measuring tape and a laser alignment toolkit that has a laser beam and safety glasses in it. Follow these steps to check the pulley alignment using it:

  • Measure the distance between the two pulley centers in question.
  • The crankshaft point is the reference point for aligning all pulleys.
  • The acceptable pulley misalignment tolerance is half of a belt rib for every six inches of separation.
  • Turn the laser on and place the tool base in the pulley grooves closest to you.
  • The beam should strike the top of the second rib of the target pulley.
  • Check the pulley run-out by rotating the pulley and see if the position of the laser changes and hits a different pulley rib.
  • If the alignment is within tolerance, reverse the direction of the beam by placing the tool on the target pulley.

Here’s how you can test the results of your diagnosis:

  • If the beam doesn’t touch the top of the ribs of the new target pulley, the pulleys have an angular misalignment.
  • If the beams are out of tolerance in both directions, they have a parallel misalignment.

Once you’ve identified which of the pulleys are misaligned, you can easily realign them by using a torque wrench to change their position. You can also take it to a mechanic if you feel uncomfortable doing this job yourself.


What components should I replace when changing the serpentine belt?

When replacing the belt, it’s a good idea to replace the tensioner, idle pulley, and tensioner pulley with the belt. Not doing so can cause you to do another replacement job soon.

Can a failing water pump cause the drive belt to come off?

If the drive belt is connected to the water pump, then a failing water pump can develop a leak and make the serpentine belt come off. But some of the water pumps are electric and they won’t cause any issues with the drive belt.

What causes excessive cracking noise from the serpentine belt?

The two main reasons behind a cracking noise coming from the serpentine belt are the belt itself is worn out and a faulty tensioner.

What does fraying of the serpentine belt mean?

If the edges of the serpentine belt are frayed, that indicates a misalignment of the pulleys. You’ll often hear a thumping or rubbing noise when the belt doesn’t sit on the pulley properly and becomes frayed.


Now you know why my serpentine belt keep coming off and how you can fix the main reasons that cause it. A bad tensioner, the serpentine belt itself wearing out, and the pulleys being damaged or misaligned are typically the most common reasons behind it.

However, it can also be caused by coolant or oil leaks, failing AC compressor or water pump. Diagnose these issues carefully following this guide and fix them. Drop a comment below if you have any more questions about common serpentine belt problems.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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