Your car has probably been a faithful servant for a while now. You’ve begun to regard it much as you do your refrigerator; it’s one of those things that does its job and doesn’t require much thought. Then one morning you start your car and an ear-piercing screech or shriek comes from the engine. People on the street look at you and neighborhood dogs begin to howl. But what's going on? A little knowledge of the systems in your car can help you figure it out.
If you've listened to this sound a few times, you may have already noticed some patterns. Does the noise occur only at start up and then go away after 30 seconds or so? Is it worse in cold weather than in warm? If so, then you are probably looking at a tired drive belt. If the noise is continuous and doesn’t stop, it could still be a belt, but your problems may go deeper.
Part 1 of 1: Diagnosing a high-pitched screech
Materials Needed
- Belt dressing or some spray lubricant
- Safety glasses
- Workshop manual
Step 1: Listen to the engine. Cars have a number of devices that require mechanical energy and are driven by rubber belts. Among those are the alternator, which maintains a charge on your battery and electrical system, the air conditioning (AC) compressor, which circulates the refrigerant for the AC system, and the power steering pump, which provides hydraulic pressure for the power steering and sometimes the brakes.
Some cars operate all these accessories with a single, serpentine belt. Others have multiple belts for the different devices. When these belts start to slip, they will make a sharp screeching noise.
Step 2: Operate the accessories. Most often, the belt screeching occurs at cold start: when the car is started after being parked for at least four or five hours. Start the car while it is cold and turn the AC off and on. If the sound of the screech changes, then the fault is likely in the belt that drives the air conditioner.
Operate the headlight switch. If that causes a change in the squealing sound, then the culprit is the belt that drives the alternator.
Turn the steering wheel to full lock position either right or left. If that changes the sound, then the belt that drives the power steering is at fault.
Step 3: Consult the workshop manual. Find a diagram for the drive belt layout. Make note of whether you have multiple drive belts or individual belts for the different accessories. With what you may have learned by operating the accessories, you might be able to pin down which belt is giving you trouble.
Most modern cars have a single serpentine belt that drives all the devices. If that is the case, any one of the accessories may be contributing to the sound of the belt.
Step 4: Lubricate the belts. With the engine running, and your safety glasses in place, shoot some belt dressing or some spray lubricant on the belts. If there is a problem in the belts the sound may stop instantly.
This is not a permanent fix. In fact, the belt might start squealing again in just a few minutes. But if the squeal stops, it’s a good indication that the noise is simply a belt and not a tensioner.
Step 5: Check the belt tension and condition. Shut off the engine and try to flex the belt with your fingers. The workshop manual will tell you how much you should be able to move it. Old style V belts may have between half and one inch of flex while modern serpentine belts will have much less.
The belt tension may be adjustable, or it may be managed by an automatic tensioner. Either way, many modern cars have very little working space at the front of the engine so replacing or adjusting the belts can be a test of your patience and ingenuity.
Look for cracks or glazing on the surface of the belts. The belts start out relatively soft, then as they age they become hard and shiny. When the belt is hard, it is more likely to slip, even under the right tension. If the belt is old and hard, there is nothing to do but replace it.
If your belts look good, and the tension is correct, or if lubricating the belts didn’t produce any results. You could be looking at belt tensioner issues or you may have one of the accessories failing and trying to lock up. Diagnosing any of these problems will involve a lot more work. In any case, calling YourMechanic can bring a professional to your home or office to help with the diagnosis or repair.
