How to Quiet a Squealing Belt on Your Car

Engine belt
 Marin Tomas/Getty Images

When you hear a loud squealing sound from under your car's hood, it's very likely that the problem is a belt that is slipping against the pulleys. Most cars today have a single, continuous serpentine belt that winds around various pulleys found on the different components on the front of the engine. The alternator, power steering pump, water pump, and air-conditioning compressor may all be connected to this serpentine belt.

Older cars may not have a serpentine belt, but they do have different V-belts that drive different systems. When any of these belts begin to slip, the resulting friction can cause a piercing squeal. 

A belt usually slips for one of three reasons: 

  • There is fluid on the belt
  • The belt is too loose
  • The belt is too tight

Fluid on the Belt

Start by simply wiping down the belt with a  cloth while the engine is off. If you notice that the cloth is absorbing a lot of liquid as you wipe the belt, it's likely that oil or some other fluid has been spilled on the belt and is causing it to slip. The remedy is simply to carefully wash, rinse, and dry the belt. If this eliminates the squealing, all is well. But you do need to consider why fluid is on the belt in the first place. It's possible it was just due to an accidental spill that occurred while you were adding motor oil, power steering fluid, or coolant.

But if the belt soon begins to squeal again, it's possible you have a leak in one of the engine components that needs to b addressed. 

A Belt That Is Too Loose or Too Tight

If there seems to be no fluid on the belts causing them to slip, the next thing to check is the tension on the belt. A belt that is either too loose or too tight will often slip against the pulleys, causing the squeal.

 

While the motor is running, pour water over the squealing belt. It the noise stops, it tells you the belt needs tightening. There is a belt tensioner adjustment that is usually located half-way down the front of the engine. Normally there should be about 3/4-inch of play in the belt, and the tensioner can be adjusted to return the belt to normal tension. A very old belt may be so worn that it's impossible to tighten it enough to stop the squealing, so if you find that this is the case, be prepared to have the belt replaced. 

A Temporary Fix: Spray-On Belt Dressing

If you're unable to stop the squeal with either of these methods, you can use a spray-on belt dressing compound, widely sold at automotive shops. It is applied to the belt while the engine is running, and you should notice that the squeal stops almost instantly. This is a temporary fix, though, and it only quiets the squeal without addressing the underlying problem. Your belt likely has another problem that needs to be addressed. It's also possible that the problem lies elsewhere is system, such as the power steering reservoir, the water pump, or the brakes. 

Applying an aerosol belt dressing is as easy as it seems. All you need to do is aim and spray.

The catch is that you have to do it with the engine running, so be very careful!

You need to direct the spray toward the inside of the belts, the part that touches all of the metal pulleys. Since the belt is moving, you only need to find one good location to spray from. Spray the entire length of the belt by holding the nozzle down for 10 seconds or so while the belt goes by.

Safety first!

  • Work on level ground with good footing so you don't lose your balance.
  • Don't wear hanging garments that could get caught in a belt and suck you in with them.
  • If you have long hair, don't lean over the belts close enough to get your hair caught.
  • When working in a running engine bay, always concentrate on the job and avoid distractions. If there is too much going on around you, wait until you can do it calmly.

Remember, this is a temporary fix.

Your belts are squealing because they're worn or loose and should be properly repaired ASAP.