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Why is My Engine Screeching?

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  1. step : Diagnosing Engine Screeching (0:05)
    • Watch your volt meter as you start the car
    • If the voltage meter changes with the screech, there is an alternator or belt problem
    • Push on the belt by hand
    • The belt should move only about 1/4"
    • If the belt moves more than 1/4", it is too loose
    • Take the belt off the alternator
    • Turn the alternator pulley to make sure it moves smoothly
    • If the alternator makes a screeching noise when you turn the pulley, it needs to be replaced
  2. step : Tightening the Belt (3:25)
    • Put the belt onto the alternator, if it is not already on
    • Loosen the alternator bolts
    • Push the alternator into place with a pry bar
    • Tighten the alternator bolts
    • Check the belt tension by hand
    • Start the engine to test the belt

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You go out to your car and you start it up, and you hear this. There's a pretty common cause of that, and I'm going to help you out and show it to you. That's actually your belt screeching, in most cases. I'm going to bring you into this car.

We're inside, and what we're looking at here is this gauge. This is your volt gauge. Most cars have it, though sometimes you just have a light that will turn on when you turn your key on. Let's watch the volt gauge. You can see it goes up to about 12 there, and you'll see it move with the screech. It's going to be subtle, but just keep your eye on it. You can see how when it screeched it went up a little bit. That's a good indicator that screeching sound is your alternator.

Now we'll look at the engine compartment on this old '74 Pontiac. Right here, this is what an alternator commonly looks like. This is a good car because it's right up here in the middle. Most cars it's up near the top; some of the newer four-cylinder cars have it mounted lower, closer to the bottom of the engine. Generally, it's an aluminum housing with a big black pulley on the front. What we want to look at here . I'm not sure if you can see. We might need a different angle. Let me just move you around here, a little bit, so you can see that belt better. This belt should have a certain amount of tension, and it doesn't have enough tension. You want to be able to press it. You should only be able to push it about a half an inch down, and I can push this a good inch or more without too much force.

We're going to take it, and on most alternators there are two to four bolts that hold them. On this one, there's a bolt here and a bolt right down here. Just loosen those. I'm going to use a big pry bar, pull on it to tighten the belt, and then tighten it back up. A note on some of the newer cars: you have automatically tensioning belts, big serpentine belts. Actually, before I tighten it up what I'm going to do . I kind of know because this is a new alternator, it should turn, but before you tighten the belt what you should do is check the alternator. You just want to take the belt off and spin the alternator to make sure it spins nice and smooth. If your alternator is going bad, that can cause a screeching noise because it can be interfering with your belt. When you spin the alternator, feel for any kind of crunching. It should just spin nice and smooth. It shouldn't make any noise. You shouldn't feel anything when you're spinning the pulley. If you are feeling anything, if it's a little bit hard to turn at all then you need to replace your alternator, and that's what is causing the screeching. If you've had an alternator that's causing your belt to screech, I recommend replacing that belt, too, because it probably could have worn that belt out.

I'll tighten this up, and then we'll start it up and see if it does the same thing. I got my tools for the job. The bottom bolt is 9/16ths. I put this on there, and I'm going to loosen that bottom bolt up. I take my nice, big pry bar. I'm going to put it in behind, get up the right angle, and I'm going to loosen this top one and pull on the alternator at the same time to tighten it, and then re-tighten the bolt. Tighten it up a couple more turns, and a little bit more. Tighten up that bottom one. Check the tension. It's better. Let's see. I'm going to start it up and hope I fixed it.

Very nice. That's it. If you hear a screeching it's either you have a bad alternator that's interfering with the belt, or your belt is just a little bit loose. I hope this helped you out. Thank you.

We hope this video helps you out. Brought to you by, your source for quality replacement parts and the best service on the Internet. Please feel free to call us toll-free, 888-844-3393. We're the company that's here for you on the Internet and in person.

Tools needed for replacement:

    Screwdrivers & Related

  • Pry Bar

  • Wrenches - Metric

  • Complete Metric Wrench Set

  • Wrenches - SAE

  • Complete SAE Wrench Set

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