Why is your car squeaking? The answer might be because of aging engine belts. Read on for information about engine belts, and how to diagnose the problem.

Bad Belts Explained

Man checking under the hood
Man checking under the hood

No one likes when the “Why is my car squeaking?” question runs through their head, but if you’ve ever owned a car, chances are you’ve been there. Now, those squeaks, squeals, creaks, and other assorted strange car noises can be caused by a wide range of issues including worn-out brake pads and belts in need of replacement.

For more info on the former, check out our Car Maintenance 101 article. Today, we’re looking at the latter, so if that squeaking seems to be coming from the engine bay, you’re in the right place.

For cars made around 1990 and later with internal combustion engines, there are generally two belts to be aware of – timing and serpentine. Both belts perform critical operations for keeping the engine running properly, so let’s have a look at the ins and outs of each.

What is a Car Timing Belt?

Timing belts are responsible for synchronizing crankshaft and camshaft rotation. Located in the bottom of the engine block, the crankshaft rotates as the pistons go up and down to generate the power needed to spin the wheels.

On overhead cam engines, the camshaft (there can be more than one) manages the opening and closing of the intake and exhaust valves. The timing belt effectively choreographs this complicated performance. This belt also commonly powers the water pump, a critical component in keeping your engine running at the right temperature as we look at here.

Timing belt teeth
Timing belt teeth

As far as identifying a problem with your timing belt, the most common audible indicator is a ticking noise. You may also notice a rough idle or smoke exiting the exhaust pipe at start-up. Unlike the serpentine belt, timing belts are hidden behind a cover, so visual inspection is a bit trickier. However, it’s worth noting that the timing belt has “teeth” running across the bottom of the belt versus the lengthwise “ribs” you’ll find on a serpentine belt.

This is because the timing belt runs between a set of gears, not smooth pulleys. Which brings up another point. Your car may very well have a timing chain as those have become more common of late thanks to their nearly lifetime durability.

If you’re unsure, take a look through the owner’s manual. In the maintenance section, cars with a timing belt will also have a manufacturer-recommended replacement interval in the neighborhood of 100,000 miles.

Mechanic checking out a timing belt
Mechanic checking out a timing belt

Given the essential nature of a timing belt, it’s worth following that recommendation because if the belt fails – read: breaks – while you’re driving, there’s a strong likelihood your engine will be permanently ruined. Like any vehicle maintenance, replacing the timing belt can be done at home, but it certainly leans to the more technical end of DIY service.

Along with the likely knuckle-busting work required to access the belt itself, putting the new one on requires exact positioning to ensure the timing of the engine is accurate. Repair manuals typically contain the nitty gritty on how this is done, but if you’re unsure, this is the kind of job a good mechanic will be very familiar with.

What is a Car Serpentine Belt?

Old and new serpentine belts
Old and new serpentine belts

The other main belt you can expect to find – on a modern internal combustion engine – is of the serpentine variety. So named for the circuitous route it runs around the engine, this belt is just as important as its timing-focused neighbor. Sometimes referred to as the fan belt or accessory drive belt, the serpentine belt is a single long rubber strap that normally provides power to the alternator, power steering system, and air conditioning compressor.

Typically, you can see the serpentine belt when you pop the hood of your car. It’ll be mounted up front, running around a host of pulleys. Some of those pulleys spin the aforementioned vehicle systems, while others – idler and tensioner pulleys – are there to provide the just-so-tautness needed to keep everything operating smoothly.

Like the timing belt, a serpentine belt is powered by the engine’s crankshaft however, underneath you’ll see a series of “ribs” running lengthwise along the bottom where the belt makes contact with all those pulleys, not “teeth”. And if you’ve decided the answer to the “Why is my car squeaking?” question can be found in the engine bay, it’s more likely the serpentine belt.

For one thing, the serpentine belt will not have a cover, so it is more prone to damage from external sources like dirt and grease. If the underside ribs become glazed or otherwise worn, they can start to slip on the pulleys and in turn, start squeaking.

Sometimes in cold weather, you may hear squeaks and squeals after start-up as the belt may be stiff from sitting overnight, but the noise may then dissipate as the belt warms up. An illuminated check engine light, which we discuss here, may also be related to a roasted serpentine belt.

The good news with serpentine belt wear and tear is that you can perform a visual inspection without much hassle. With the hood open – and engine off – you can shine a light down in front of the engine to have a look at the belt condition.

Replacing a serpentine belt
Replacing a serpentine belt

As we note in this explainer article for taking a car out of storage, telltale signs of wear include cracks, abrasions, rib separation, fraying, shiny spots, and too much slack. To test that slack, press on the belt in a section between two pulleys. You should be able to move it about a half inch.

Replacing the serpentine belt is lower on the DIY difficulty scale compared to a timing belt. It’s worth consulting a repair manual for specifics but essentially you will need to remove the tensioner pulley and then slip off the old belt. Take care to note the route before removing it and then reverse the process with a new serpentine belt.

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Niel Stender

Niel Stender grew up doing replacement work on his 1990 Cherokee and 1989 Starion, so it’s not surprising that he would put his mechanical engineering degree from the University of New Hampshire to use in the car world as a vehicle dynamics engineer. Now engineering sentence structures, his writing infuses his auto experience with his time in marketing and his sales experience. Writing about cars for close to a decade now, he focuses on some of the more technical mechanical systems that are found under the hood and throughout a vehicle.

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