Does your car make an awful squealing noise that likely wakes up the neighbors when you first start it up on cold mornings? Maybe it happens when you’re accelerating from a stop light or driving through a puddle? It’s likely your serpentine belt.
The squealing noise isn’t just embarrassing, it’s a sign that can help prevent bigger problems down the road. The good news is that many belt problems are relatively simple and inexpensive to fix. Let’s look at what causes this.
A serpentine belt (also called a drive belt, accessory belt, or fan belt) is a long, winding belt that powers multiple engine components like your alternator, power steering pump, air conditioning compressor, and water pump.
While "fan belt" is an older term from when these belts only drove the cooling fan, modern vehicles use a single serpentine belt to drive multiple components. For a more detailed explanation of serpentine belts and how they work, check out our serpentine belt guide.
Related: Serpentine Belt vs Timing Belt – What’s the Difference?
Common Causes of Serpentine Belt Squealing
A squealing serpentine belt can be caused by several different issues. Some are quick fixes while others might require replacing parts. Here are the most common reasons your serpentine belt is making that annoying noise.
1) Loose Belt Tension
The most common reason for belt squeal is improper tension. Your serpentine belt needs to be tight enough to grip the pulleys properly. If it’s too loose, the belt will slip on the pulleys, causing that distinctive squealing sound. This is especially noticeable during cold starts and when the engine is accelerating.
Cold weather makes the problem worse because rubber contracts and becomes less flexible in low temperatures. When you first start your car on a cold morning, the cold belt is stiffer and may not grip the pulleys as well until it warms up. This is why belt squeal is often loudest during the first few minutes of operation on cold days.
Most modern vehicles use an automatic tensioner to keep proper belt tension. Over time, these tensioners can wear out or get stuck, preventing them from doing their job. Some older vehicles use manual adjustment methods that need periodic tightening as the belt stretches with age and use.
2) Water or Other Fluids
Getting your serpentine belt wet, like when driving through puddles or after a car wash, can cause temporary squealing. This usually stops once the belt dries off. However, if your belt squeals frequently when it’s not wet outside, you might have a fluid leak dripping onto the belt.
Common sources of fluid leaks include power steering fluid, engine oil, or coolant. These fluids can damage the rubber belt over time and cause it to slip. If you notice fluid on or around your belt, you’ll want to track down and fix the leak before replacing the belt.
3) Belt Is Worn Out
Like most car parts, serpentine belts wear out over time. The rubber compound deteriorates, the belt material gets hard and brittle, and the grooves that grip the pulleys become worn down. A worn belt is more likely to slip and squeal, particularly in cold weather when the rubber is less pliable.
Look for signs of cracking, fraying, or missing chunks of rubber. Run your finger along the grooved side of the belt… if the grooves feel smooth or worn down, it’s time for new belt. Most serpentine belts last between 60,000 and 100,000 miles, though this varies by vehicle and driving conditions.
See Also: 7 Timing Belt Replacement Tips (for DIY Mechanics)
4) Bad Pulley Bearings
Each pulley that your serpentine belt runs over contains bearings that allow it to spin smoothly. When these bearings start to fail, they can cause the pulley to wobble or not spin freely. This creates friction and can cause the belt to squeal, especially during startup or when the engine is accelerating.
The most common pulleys to fail are the idler pulley and tensioner pulley since they spin at high speeds but don’t power anything. You can check for bad bearings by spinning each pulley by hand (with the engine off). If you feel any roughness, wobble, or hear grinding, that pulley needs to be replaced.
5) Belt Misalignment
When your accessory belt isn’t properly aligned with all its pulleys, it can cause squealing and premature wear. Misalignment often happens after a belt or pulley replacement if components weren’t installed correctly. It can also occur if an accessory bracket gets bent or if motor mounts are worn, allowing excess engine movement.
You can sometimes spot misalignment by looking down the length of the belt while someone else turns the crankshaft by hand. The belt should track straight without moving side to side on any pulleys. Some auto parts stores sell laser alignment tools that can help identify this problem.
6) Glazed Belt Surface
A glazed belt happens when the rubber surface becomes hardened and shiny, usually from excessive heat or slipping. When this happens, the belt loses its ability to grip the pulleys properly. While glazing often occurs alongside other problems like misalignment or improper tension, it can also happen if you regularly drive in very hot conditions.
Once a belt becomes glazed, it will need to be replaced. You can prevent glazing by maintaining proper belt tension and fixing any alignment issues quickly. If your belt starts squealing, don’t ignore it. The longer it slips, the more likely it is to develop a glazed surface.
Diagnosing the Problem
Before you start replacing parts, it’s helpful to narrow down exactly what’s causing your belt to squeal. Here’s a systematic approach to finding the source of the noise.
Step 1: Visual Inspection
First, pop the hood and look at your serpentine belt. Check for obvious signs of wear like cracks, fraying, or missing pieces of rubber. Also look for any fluid leaks that might be dripping onto the belt. While you’re there, check that all pulleys are properly aligned.
Step 2: Belt Tension Check
Push on the longest straight section of the belt with your thumb. There should be about a half inch to an inch of give. If it moves much more than that, your belt is likely too loose. Also check if your automatic tensioner moves freely. If it’s stuck or moves roughly, it needs replacement.
Step 3: Spray Bottle Test
If the belt looks okay and tension seems right, try this simple test: With the engine running (be careful of moving parts!), lightly spray a small amount of water on the grooved side of the belt. If the squeal temporarily gets louder, you likely have a tension problem. If the squeal goes away, you might have a misalignment issue.
Step 4: Check the Pulleys
With the engine off, try spinning each pulley by hand. They should turn smoothly without any grinding noise or wobble. Pay special attention to the idler and tensioner pulleys since they’re most likely to develop bearing problems.
Repair Costs
The cost to fix a squealing serpentine belt varies quite a bit depending on what’s actually causing the problem. In general, here’s what you can expect to pay:
Belt Replacement
A new serpentine belt typically costs between $25 and $75. Professional replacement will add about an hour of labor, bringing the total to $100-200. Some vehicles have more difficult access to the belt so the cost of labor could be more. A higher cost is also likely if you have a dealership do the job.
DIY
If you’re mechanically inclined, replacing the belt yourself is fairly straightforward on many vehicles, but physical flexibility matters. You’ll often need to reach up and around engine components, sometimes from awkward angles.
Access is typically from underneath the car (requiring a jack and jack stands) or by reaching down from above. If you have trouble bending, reaching, or working in tight spaces, you might want to leave this job to a mechanic.
You’ll need a socket set and possibly a serpentine belt tool to release the tensioner. Some vehicles require removing other components to access the belt, which can make the job more challenging.
Tensioner Replacement
If your automatic tensioner is the problem, expect to pay $25-50 for the part itself. Labor usually runs 1-2 hours since the tensioner can be tricky to access on some vehicles. Total cost at a shop: $150-300.
Pulley Replacement
Bad idler or tensioner pulleys usually cost $20-40 each. Labor time is similar to a tensioner replacement. Total cost at a shop: $125-250 per pulley.
Fixing Fluid Leaks
If your squeal is caused by fluid leaking onto the belt, costs can vary widely depending on the source. A simple power steering hose might only cost $200 to replace, while a major oil leak could run into the thousands if seals need replacement.
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Mine is also making a loud noise when I turn the car on with the remote start and the heat is on, if I turn the heat off it stops. Is it dangerous to drive if I don’t get it fixed right away?
If it’s the serpentine belt, it could leave you stranded if it snaps.
why does a car make lots of noise when driving when it is very cold outside…?
What kind of noise is it making?
like this: rrrrrrrrrorororororororo rororororo pfrrrrrrrr chirrrrrrrrr…chirrrrrrrororororororororororororororororororororororororooor pfrrpfrssss… lol
lol
Does this noise ever go away? Are you referring to a cold start where in order to get the engine and catalytic converters warm faster the ecu adjusts the air/fuel ratio to run rich which burns more fuel and the exhaust will make more deeper grumbles. It really does roar to life when cold if thats what you mean