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Engine Timing

Tensioner Troubleshooting Guide

Tensioners, like any other part, don’t last forever, and automotive technicians will be replacing more and more of them.


A failed tensioner can cause the belt to break or fly off the drive, resulting in a breakdown. Often the cause is misdiagnosed as a belt problem, when in reality the tensioner should be replaced.

The key symptoms that can indicate tensioner wear are as follows:

1. Appearance/Worn Pulley

  • For steel idlers, paint has worn off the belt tracking area - this is a normal condition and no corrective action is required.
  • Plastic idler pulley appears to be worn on belt tracking area - may be due to extreme environmental wear (i.e., heat, water, stones) and the idler should be replaced.
  • On plastic idlers, pulley is chipped - may be due to stone damage or faulty installation practices. Idler should be replaced if the chip is in the belt tracking area.
  • On steel idlers, pulley has been marred in belt tracking area - may be due to stone damage or faulty installation practices. Idler should be replaced if the deformation is in the belt tracking area.
  • Pulley shows signs of corrosion - may be due to the coating on the pulley having worn off. Idler should be replaced.
  • Idler has excessive wobble (free rock) - may be due to bearing failure, excessive load on pulley, or belt not tracking properly over pulley. Idler should be replaced.

2. Tensioner Appearance

  • Tensioner arm is cracked - may be due to excessive force used in removal, long-term fatigue failure, or tensioner being allowed to snap back into stop position. Tensioner should be replaced.
  • Tensioner vibration during engine idle is excessive - tensioner damper may be worn or accessory may be out of round. Tensioner should be replaced.
  • Grease appears to be leaking out of the bearing - may be due to grease purge, seal degradation or excessive radial internal clearance in bearing. Idler should be replaced.
  • Bearing seal is missing or damaged. Tensioner tilted or misaligned, or gap exists between tensioner arm and base - may be due to worn pulley, environmental damage (i.e., heat, water, stones), or poor tensioner mounting. Idler should be replaced if worn, or if tensioner is damaged, whole tensioner unit should be replaced.


3. Loose, Sticking or Seized Tensioner

  • Tensioner does not operate smoothly - bearing surface or damper may be damaged, or spring is broken. Tensioner should be replaced.
  • Pulley is seized and will not rotate freely - bearing may be damaged. Idler should be replaced.
  • Pulley does not rotate smoothly or has a sticky feel to it when spun - radial internal clearance in bearing is too low or bearing fit in pulley is tight. Idler should be replaced.
  • Pulley and bearing have relative motion - bearing is not being constrained in idler pulley. Idler should be replaced.

4. Noise

  • Belt squeal noise - belt worn or stretched to maximum take-up length of system, or tension force not sufficient. Check belt length window. If belt is correct length, replace tensioner.
  • Tensioner clatters or rattles during engine operation - damper is worn, or bearing surfaces within tensioner are worn. Tensioner should be replaced.
  •      Belt chirping due to system misalignment - pulley or tensioner are worn, cracks in tensioner base or arm, or mounting bolts loose. Replace worn or cracked tensioner. Tighten loose bolts to vehicle manufacturer’s specifications. Check entire system for misalignment.
  • Pulley makes a high-pitched whine or hooting noise after the engine is started. Noise lasts up to three minutes - may be due to worn bearing, or bearing fit to pulley is incorrect. Idler should be replaced.
  • Pulley exhibits noise during normal operation - bearing is not functioning properly. An idler pulley is normally very quiet. Idler should be replaced.
  • Pulley and bearing assembly rattle when shaken - bearing cage is broken, balls in bearing are loose, or no lubricant in bearing. Idler should be replaced.

5. Bearing Noises/Bearing Hoot

  • Continuous hissing and grinding noise that gets louder as engine RPM increases - no bearing lubricant. Use an automotive stethoscope to locate the source of the noise. Turn engine off and hand spin pulley. If it’s hard to turn, feels rough or rattles, replace pulley assembly.
  • Continuous growling noise that changes to a whine as engine RPM increases - a bearing is about to fail, excessive idler pulley wobble, or contamination of other fluids into pulley seal has occured. Visually inspect bearing in question for signs of heat “bluing” of metal or grease purge. Check for bracket movement due to loose or misaligned fasteners. Check for proper belt mounting.
  • Hoot noise that occurs at low temperature (below -20° F) - may be due to insufficient or improper bearing grease. If belt has glazing, cracks or other visible defects, replace belt.

6. Belt Tracking

  • Belt does not track properly on idler belt tracking surface - bearing is not fixed to the correct depth in pulley, belt tracking surface is not square to bearing mounting surface, or pulley tracking surface is tapered (NB: crowning or bowing of belt tracking surface is sometimes intentional). Idler should be replaced if faulty.









When diagnosing belt drive faults and failures, it is essential to check all components in the belt drive system, including tensioners for signs of wear and damage. By checking all components and replacing them where necessary, the belt drive will function more smoothly and over a longer lifetime. When replacing components it is strongly recommended to use OE equivalent parts such as those supplied by Gates, to ensure optimum quality and lifetime.


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