A serpentine belt is a sturdy belt used to transfer power from the crankshaft to other accessories within the car that need torque. These components range from the alternator, a vacuum pump, the AC pump, a water or coolant pump, a hydraulic pump, and, traditionally, the fan.
Even though many modern designs are shifting to using electric motors to power most of these things, the alternator still needs the serpentine belt.
When new, the belt is tight and maintains perfect contact with the pulleys it runs. Over time, the belt stretches, and the idler pulley or belt tensioners can’t compensate enough starts slipping. As it slips, it rubs against the pulleys leading to the squealing noise.
Moisture or contamination from other fluid spills could reduce its frictional characteristics, making it slip.
Top Causes of a Serpentine Belt Noise
A squealing serpentine belt means it is slipping. The cause of the slip could be:
- A misaligned belt
- An aged belt
- A loose belt
- A faulty pulley or auxiliary device
- Contaminated belt surfaces
Here is a detailed breakdown of all the possible problems that make your belt make that annoying noise.
Normal Wear and Tear
Most serpentine belts have an average lifespan of 50 to 100 thousand miles. The grooves and friction surface on the belt that improve friction will wear out as time goes by.
This, coupled with fraying and additional damage to the edges of the belt, impairs its ability to make perfect contact with pulleys. It will slip more often.
Old belts will have missing rubber on the ribbed side. Moreover, the belt will be thinner than a new one. You can tell if you’ve worked on cars before. If not, compare it to a new one (regardless of the car model)
Alternatively, you can use a belt gauge to find
A Misaligned Tensioner or Pulley
Misaligned pulleys and tensioners could throw the belt slightly off track. This will make the belt wear out unevenly or give the back a hard glazed surface that isn’t a good friction surface.
The now compromised serpentine belt could also get less tension from the pulleys and tensioners. The result would be poor contact with the driving pulley and the pulleys on driven accessories.
You will hear more squealing, and if it is bad enough, some accessories won’t hit the correct RPM for efficient performance.
Prevailing Weather Conditions
If your belt squeaks when you turn on the car and the noise goes away when the engine warms up, then you shouldn’t be worrying. Moisture and condensation on the belt are causing it to slip and create noise.
Morning dew, fog, and even spills within the engine bay contaminate the belt. Unless a chemical degrades the belt’s rubber, the problem should go away as soon as the heat evaporates off the liquid.
Note that cold temperatures also stiffen up the rubber in the belt. A less pliable belt won’t conform to pulleys well and has less friction properties. This should go away as soon as the engine spins and the belt warms up.
Grease and Oil Contamination
Just like moisture from ambient weather, grease and oil contamination will also make your serpentine belt slip and squeal.
If you worked on your car recently and some fluid spilled onto the belt, that could cause the noise.
Unexpected contamination could happen when your engine is leaking oil – especially on the side where one of the driven pulleys or the crankshaft is leaking oil.
Even though the serpentine belt might burn off the spill as you drive, inspect your engine and fix any unexpected spills. You don’t want to drive around with your engine leaking oil or coolant.
A Damaged Tensioner Belt
The belt tensioner is a spring-loaded arm with a pulley that picks up any slack on the belt. You can check it by removing the belt and using a wrench to move the tensioner arm through its entire motion range.
The movement should be smooth and fluid. A good tensioner only moves up and down, not to any side.
Suppose the tensioner wiggles or there is a loose chatter in the belt tensioner. In that case, the loose movement will lead to occasional slipping since the tensioner isn’t maintaining enough tension on the belt.
While most tensioners are spring-loaded, some use hydraulic fluid to hold the correct pressure against the belt.
How to Adjust a Loose Belt Tensioner
Either way, an adjustable tensioner will have an adjustment bolt. Here is a quick breakdown of how to tension a loose tensioner:
PS: Consult your user manual for more detailed instructions
- Find and loosen the adjustment lock bolt and the belt pivot bolt. They’re often on the alternator
- Tighten the adjustment bolt slowly until it is at the recommended tension
- Tighten the adjustment lock bolt to hold the belt tension in place
While it’s normal for the belt to loosen over tens of thousands of miles, there are times when you can’t tighten the belt anymore. This could be due to a damaged tensioner or a worn-out belt.
If you have to keep tightening very often, it is time to start replacing the components.
Defective Bearings
Sometimes, the squealing isn’t all about your serpentine belt. While its slippage could be the common cause for the noise, it could have a bearing in one of the driven components that is the problem.
Using the Water Check to Troubleshoot and Isolate the Noise
With the engine running, spray some freshwater onto the serpentine belt. Enough water should lubricate it. While it will still be slipping, it won’t make the squealing noise.
If you can still hear the squealing noise after spraying the belt, chances are it is from worn pulley bearings.
Better still, you can replace the belt and see if the noise persists. If it does, you will have to inspect all driven components and find which one could be the culprit.
A Defective Driven Component
Finally, the problem could be one of the driven components that draw power from the serpenting belt.
A stuck AC pump or alternator could force a well-tensioned belt to slip. If this happens, you will notice that the accessories controlled by the damaged component aren’t working.
For instance, your alternator won’t be spinning, and you will run out of power. If it is the AC pump, then your air conditioning will not blow cold air at all.
Inspect all driven components and ensure that they are all spinning freely. If they are not, you have your culprit right there.
How to Fix a Squeaky Serpentine Belt: They Myths and Truths
Most DIY mechanics or professionals always replace the serpentine belt instead of trying additives to stop the squealing.
In a car past 50K miles, a replacement is a first and most reasonable step to fixing the problem. Here are some ideas on how to permanently or temporarily fix the problem.
Use a Squel Spray
The market is awash with different spray compounds designed to reduce belt noise. The direction is to use them on the ribbed section of the belt to regenerate the belt and improve friction.
A great deal of them use lubricants and tacky elements to make the belts more pliable and sticky.
While this might fix the problem quickly, the compounds could make the different layers in the belt disintegrate, making the belt fray and tear faster.
Avoid these temporary fixes unless absolutely necessary.
Fixing a Noisy Serpentine Belt With Bar Soap
Sometimes, your belt might be squeaking because it’s dirty, oily, or greasy. Applying bar soap on the ribbed side of the belt might get rid of this gunk, sorting out the problem.
Note that this temporary problem won’t work if your belt is old and needs replacement. Only use it if you see visual spills on a relatively new belt.
Cleaning might fix the problem for a while. However, finding the source of the contamination and fixing it will lead to a permanent fix. It will also be in the best interests of your engine.
Tightening and Aligning the Belt
If you recently replaced the belt or had any of the components the serpentine belt drives services, chances are you did not tighten the serpentine belt to spec.
This is an easy fix if you are confident that the belt is new, not damaged, and clean. Follow the tensioning instructions specific to your car model or follow the general guide we listed out in the section on troubleshooting and fixing a loose belt tensioner.
Repairing and Replacing Damaged Bearings or Components
Finally, you can fix your squeals by identifying and repairing any damaged component with damaged bearings or something keeping the pulley stuck.
Apart from running the water test, you can remove the belt and individually spin each component, listening for the noise. Anything with a slight squeal or that seems jammed will need fixing or replacement.
Can You Spray WD40 on a Serpentine Belt?
While WD40 will remove moisture from metal and plastic, it will most probably damage some of the rubber components on your serpentine belt. If you are lucky, the noise will temporarily disappear before coming back again. It could even make it worse if the damage on the rubber is fast.
How Long Will a Serpentine Belt Last After it Starts Squeaking?
You can drive your car with a squeaking serpentine belt for thousands of miles if lucky. It could also depreciate fast and snap within hours or even minutes of squealing.
It all depends on what type of damage is making the belt squeal. An old belt that is misaligned will fray and split fast. A belt in good condition squealing because the tensioner is slightly loose will keep going for thousands of miles – as long as it makes enough contact to keep crucial components spinning.
Rule of the thumb: Have the serpentine belt and all other components it touches inspected as soon as you hear the squeak. You wouldn’t want the belt failing while out on the open roads.
How Far Can You Drive Without a Serpentine Belt
Well. Not very far. A couple of things will start going wrong depending on how your car is configured. The most notable is you will start losing power since your alternator will no longer be generating any.
Electronics in the vehicle will soon start failing, and your car will grind to a halt. Check this post we did about driving your car without an alternator for more insight.
Other than losing electricity, you will also lose:
- Power steering in vehicles using hydraulic power steering systems
- Brake boost in diesel cars that run an independent vacuum pump
- You AC will fail since the AC pump won’t be running
- Your car will overheat if you have a mechanical water pump that runs off the serpentine belt