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How To Diagnose And Fix A Serpentine Belt Under 45 Mins


Serpentine Belt Diagnosis

Is your vehicle making squealing noises whenever you start the engine? It can often become discomforting, but more importantly, it is an indication of something wrong with your engine. Mostly, it is the sound of a bad serpentine belt, also known as the drive belt. A serpentine belt is a closed-loop reinforced rubber belt that is wound around a system of pulleys and powers various parts of the engine, like the power steering pump, air conditioning compressor, water pump, etc. A serpentine belt keeps the engine accessories running smoothly and efficiently by providing a continuous supply of power from the engine crankshaft to all the accessories. It can wear out with time and create strange squealing or whining noises from the engine compartment.

The serpentine belt can produce noises due to several reasons like regular wear and tear, oil leaks, bad tensioner assembly, noisy pulley bearings, etc. You can simply replace the serpentine belt, but it does not guarantee that the squealing noise will go away because the issue can be somewhere else as well. Often, people avoid finding the root cause and use serpentine belt dressings to get rid of the noise, but this is a temporary solution. In worse cases, the belt can snap, causing the power steering system to stop working, which can be very dangerous. This simple step-wise procedure will help you diagnose the actual issue and fix your squealing serpentine belt.



Tools Required To Diagnose Your Squealing Serpentine Belt

Step 1. Examine the Serpentine Belt For Replacement (Under 15 minutes)

Before proceeding to the diagnosis and fixing the problems related to a squealing serpentine belt, it is important to examine it first to see if it is functional and in the proper condition or not.


Inspect The Belt Manually

  • If the serpentine belt of your vehicle looks overly deteriorated and has visible signs of wear and tear like cracks on its surface, which indicates poor condition, get it replaced immediately.
  • If you see minor cracks along the ribbed side of the belt, it is fine. If the cracks are wide (approximately 3 millimeters apart) or you see a few rubber pieces missing from the belt, it has reached the end of its life and has to be replaced.
  • Look for glazing on the top of the belt (smoother side with no grooves). Friction between the belt and pulley can lead to glazed spots, causing slippage, chirps, or belt squeaks.
  • Check the belt tension by finding the longest run between the two pulleys and pressing the belt down. If the belt is in proper condition, it should be taut with less than half-inch of play. Excessive play can indicate a worn-out belt.


Inspect The Belt Using A Belt Wear Gauge

A belt wear gauge is a simple tool that consists of teeth. The tool is pressed against the ribbed side of the serpentine belt to check for any play or lateral motion. If any motion, free rock, or play exists, it indicates that the belt ribs have worn out. If the gauge and the teeth remain tightly seated, the belt has sufficient service life.


    • Ensure the engine is off and place the belt wear gauge with its teeth matching the grooves of the serpentine belt.
    • Once the wear gauge is seated, hold it in place and rock the gauge gently and look for any play.
      • If the gauge remains seated firmly in the grooves of the belt, the belt is fine. Also, the gauge will sit slightly above the belt's surface, indicating that the belt is in good condition and can be used.
        • If you notice that the gauge rocks laterally or is seated completely inside the grooves of the belt, it means the materials have worn out enough and the belt needs to be replaced.
          • Modern EPDM (Ethylene Propylene Diene Monomer) belts do not crack often and it is hard to find signs of wear and tear with the naked eye, using the traditional methods. This is when a belt wear gauge comes in handy to spot a worn-out belt which can go unnoticed otherwise.


            Step 2. Check The Pulleys For Misalignment (Under 10 minutes)

            • First, start the engine and open the hood of your vehicle.
            • Get a water spray bottle and squirt some water on the ribbed side of the serpentine belt. You can also do this by spraying the water on the grooves of any pulley.
            • If the belt stops squeaking, it indicates that the pulleys and bearings are fine. The squeak might be caused due to a bad belt or pulley misalignment.
            • In a few minutes, if the belt will start to squeak again when the water dries out, indicates that one of the pulleys is misaligned.
            • If the belt squeaking gets louder after spraying the water, probably the belt tension is too tight or too loose. This can happen due to a bad tensioner assembly, or a stretched-out belt due to age, and they have to be replaced.


            Step 3. Check The Belt Tensioner Assembly (Under 30 minutes)

            • While the serpentine belt is on the engine, give it a small tug with your hand to see the tensioner move. If it doesn't move or fully retract back to its original position, offering a decent tension on the belt, it might be faulty, making the belt squeak.
            • Remove the serpentine belt from the pulleys. Using a socket wrench, move the tensioner arm through its total range of motion to ensure there is no sticking, binding, or notching movement. The tensioner's arm should move up and down without any lateral movement. If you see any lateral movement, it could be a bad bearing and the belt tensioner needs to be replaced.
              • Check the tensioner pulley for a free rotation, no grinding noises, and no side-to-side movement or rocking. If you see any of these signs, the tensioner pulley might be the culprit and should be replaced.
                • If your vehicle is equipped with a hydraulic tensioner, ensure the hydraulic cylinder isn't leaking.



                  Step 4. Align The Pulleys (Under 30 Minutes)

                  Using A Laser Pulley Alignment Tool (Under 30 Minutes)

                  • Before you begin the alignment process, ensure the engine is off, the serpentine belt is removed and the electric fans on the radiator are disconnected.
                  • Turn on the pulley alignment laser tool and place the tool right in the middle of the grooves on the crankshaft pulley.
                  • Place the target tool (the other part of the laser alignment tool) on the pulley that needs to be checked.
                  • Rotate the target pulley and observe if the laser is shining on the target. The laser should meet the target tool right on the dedicated center marking. This indicates a properly aligned pulley.
                  • Repeat the same process for other pulleys by placing the laser tool on either the crankshaft pulley or the pulley you just checked and is perfectly aligned.
                  • While you check a pulley using the laser tool, rotate the pulley to see if the light moves up and down across the grooves of the pulley. If it does, it indicates a misaligned pulley, which can be caused due to a bend or broken bracket, loose bolts, and damaged pulley bearings.
                  • Ensure all brackets and bolts are tightened snug to the mounting surface. Check all the pulleys by hand if they rotate freely and have no excessive play, free-rock, or grinding noise. If it shows these signs, the pulley or the bearing has to be replaced.


                  Fix Misaligned Pulleys Manually (Under 30 Minutes)

                  • Open the hood and start the engine.
                  • Observe each pulley and see if the serpentine belt is riding straight or moving side to side. Also, watch the edge of the pulley to see if it's running straight.
                  • While observing each pulley closely, hear if the noise is coming from that particular area or not. Try to figure out if the noise is coming from the left, right, underneath, or from the top of the engine, and try to locate the pulley which you suspect is making the noise.
                  • If the belt is wobbling back and forth or the pulley is not spinning straight and wobbling, the pulley may be misaligned, which can cause the belt to squeal.
                  • Also, check if the belt is running in the center of the pulley and is not running off to the side. Usually, a bad tensioner bearing makes the tensioner pulley tilt and allows the belt to run off from the center. In such a case, get the pulley or the assembly replaced.
                  • Use a mechanic's stethoscope to check for noises in the pulley bearings while the engine is running.
                  • Turn off the engine and remove the serpentine belt.
                  • Shake and spin each pulley to check if there is excessive play or noise. Any play or back-and-forth movement indicates a bad pulley bearing. This leads to misalignment, belt squeaks, and the pulley should be replaced.
                  • Ensure all mounting bolts and brackets are properly tightened and are not bent as it can also allow the pulleys to tilt and misalign.




                  As we learned above, fixing a squeaky serpentine belt isn’t just about replacing the old belt with a new one. With several components that work in conjunction with the belt, the squealing noise can originate from any faulty component which can go unnoticed while carrying out a temporary fix. Often, people end up with their new serpentine belt squeaking weeks after replacement, making a proper diagnosis is necessary. A stepwise and thorough serpentine belt diagnosis procedure that hardly takes much time can be very helpful in spotting pulley alignment issues, worn-out pulley bearings, and other faulty components. This saves you from a potential failure and gets you acquainted with the actual condition of the engine parts, so you carry out a timely replacement.

                  John Framigllia
                  Technical Writer
                  Our technical writer is known for simplifying automotive parts and services. Intuitive with various vehicles and manufacturers, he knows how to simplify complicated problems.