Serpentine Belt

Driven by the crankshaft, the multi-ribbed serpentine belt powers engine accessories such as the alternator, air conditioning compressor, power steering pump, and, sometimes, the water pump.

The days of having three or four belts on the front of an engine are mostly over, and those ‘drive belts’ have been largely replaced by a more advanced, stronger, simpler, and more reliable version -- the serpentine belt.

Ordinary drive belts go from the crankshaft pulley to one or two pulleys that need to be belt-driven. The serpentine belt winds around all of the pulleys that need to be belt-driven, and connects them all to the crankshaft simultaneously. This is where the serpentine belt gets its name because it winds one long piece of material around all of the pulleys like a snake, or serpent.


Unlike the older ‘V-shaped’ drive belts, the serpentine belt has multiple ribs that run along the pulleys of the engine accessories, and those ribs provide superior friction and tracking to ensure proper operation of all driven components. This characteristic has earned the serpentine belt the common name ‘multi-ribbed belt’.


As the engine is running, the crankshaft pulley spins at engine speed, and, since the serpentine belt is pulled tight against the crankshaft pulley and all accessory drive pulleys, engine power is transferred to all of the accessories. This may include the alternator, air conditioning compressor, power steering pump, water pump, supercharger, or smog pump.


Unlike the older style of belts, the serpentine belt does not typically require adjustment, ever. It simply must be replaced when worn out, and the automatic serpentine belt tensioner will hold the proper amount of tension on the belt under all driving conditions and engine speeds.


Symptoms of Wear or Failure of the Serpentine Belt

  • Loss of battery voltage triggers the battery warning light
  • Power steering suddenly stops functioning
  • Vehicle's engine begins overheating
  • Illumination of the check engine light
  • In some vehicles the brakes may become more difficult to press
  • The belt may be cracking, frayed at the edges, visibly worn, torn, or missing

Serpentine Belt Related Repair Advice:

  • Serpentine belt replacement intervals are different for many makes and models of vehicles, and the serpentine belt should be serviced in accordance with the owner’s manual.
  • If the serpentine belt is broken or missing, the pulleys should all be inspected for possible damage, including the idler pulleys and serpentine belt tensioner pulley
  • The serpentine belt tensioner is spring loaded, on most models, and that spring may wear over time. If this occurs, the belt may squeal under heavy load or when cold, and there may be a knocking or rattling sound from the front of the engine
  • There are several different types of materials used in the manufacturing of serpentine belts, and superior products should be selected for enhanced longevity and reduced slippage

The serpentine belt should be changed when the service interval dictates, regardless of physical condition  

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