Anonymous asked in Cars & TransportationMaintenance & Repairs · 8 months ago

would a worn alternator belt cause a low humming/whine noise especially in morning when cold and engine is warming up? why? how serious?

or if it is the bearing, how would I know? and how difficult is it to take the belt off and put it back on tight again? (have never done, it , but it looks a bit tricky and like something you might not get back on right? or might take a while to figure it out ? or am I wrong?)

7 Answers

  • Anonymous
    8 months ago
    Favorite Answer

    Try having someone who can hold a wrench loosen the adjusting bolt on the alternator and pull it tighter and then tighten the adjusting bolt.

    . The hum is from the alternator belt vibrating like the LOW guitar string as it vibrates. The whine is the squeal of burning rubber as you spin your tires on the road...except it is the alternator belt slipping in the pulleys so rubber against smooth metal....if you don't believe me get a container of tap water or a garden hose and direct a dribble of water onto the belt so it gets in the "V" groove of the pulleys. The squealing stops.

    Don't worry about water getting on the belt, after all every time you drive on the highway in the pouring rain at Highway speed, rainwater was being jammed into the engine compartment at Highway speed so everything gets wet. This dries off on a hot engine.

    Too loose of a belt means the alternator is not being turned, so not charging the battery. The slipping fan belt heats up and melts off. No slipping means no heat build up. Jamb in some wood between the alternator and the engine to give you some leverage to make the belt tighter. You won't hurt the alternator bearing...and you won't snap the belt. If you snap the belt, it was rotten. Get a new belt...and make tight. Then you are just another car on the road. None of them squeal. Unless they too have a loose belt or worn out brakes.

    • 8 months agoReport

      so, that is reason I am more worried about the bearing seizing all of a sudden and breaking the belt and water pump not working after

  • hart
    Lv 6
    8 months ago

    in the morning the aged battery get recharged

    so the loose belt is squishy

  • M.
    Lv 7
    8 months ago

    Do you have v-belts?

    Generally, an unacceptable (loose/worn) belt slips. And that slippage makes a screeching sound.

    Some belts lose pieces before they totally fail and come off the pulleys. They make sounds, but generally not humming sounds.

    Humming is generally the sound of a bad bearing. The noise gets louder and louder and one day something bad happens. The bearing could seize (stop turning), or it could suddenly disintegrate into pieces.

    Trained mechanics know what various sounds mean.

    If you take the belt off the alternator pulley and turn the pulley by hand, you can generally feel/hear a bad bearing.

    Check the serpentine belt idler pulley or tensioner pulley by hand too. Those bearings fail regularly.

    I use a 2 ft piece of broomstick with one pointed end to touch to non-moving objects to listen to the sound that they make while operating. This may be dangerous for a beginner.

    -Engine overhaul mechanic and general automotive mechanic since 1972. Retired in 2018.

    • M.
      Lv 7
      8 months agoReport

      With the engine idling and the headlights on, the battery voltage should be around 14.4 volts. If a diode is shorted, the voltage will be less, and the alternator current output will be less.

      We generally get an idea of the charging system performance by measuring alternator voltage and current.

  • Anonymous
    8 months ago

    Without actually listening to your car ourselves we can't properly diagnose it. Worn or loose belts usually squeal, they don't whine. If you've never tightened a belt, it's not rocket science but it can be tricky depending on the car. If a belt gets too worn it must be replaced. If your car has a serpentine belt, you must replace it because you cannot tighten it. Also, a serpentine belt has at least one tensioner pulley and possibly one ore more idler pulleys. These can become noisy when the bearings get worn. Just bite the bullet and take it to a mechanic for diagnosis. Ask if they would show you how to evaluate the noises and the belt condition yourself for future reference if you don't have an experienced friend that can teach you. .

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  • 8 months ago

    If you have to ask, you shouldn't be messing with it. Belts usually don't whine, especially serpentine belts.

  • Anonymous
    8 months ago

    Usually, that would make a high pitched squeal. Maybe a whine. You may be able to drive on it for a long time. Or, the belt could break tomorrow. When it breaks, you will need it fixed before you can go again. I'd take it in and have someone do it. It shouldn't be expensive and likely isn't worth the hassle of doing it yourself.

  • 8 months ago


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