Serpentine belts, sometimes called fan belts, are long, flexible belts that power many of the accessory devices attached to an automotive engine. These include the alternator, water pump, air conditioning compressor, air pump and power steering pump in most vehicles. Before the 1980s, vehicles used a series of belts, but a single belt was found to be more efficient and to increase the life of the belt.
A squealing fan belt manifests itself at different times and in different ways. The belt may squeal or chirp constantly in cold, wet or moist weather. The belt may only squeal when the vehicle is accelerating. In both cases, the belt is most likely slipping on the pulleys it is wrapped around. This usually happens when the belt is worn out. Over time, heat and constant tension permanently expand the belt, necessitating its replacement. Check the belt for signs of cracks or peeling; these are indications the belt needs replacement.
Even after a new fan belt is installed, squealing may continue. This occurs when the old fan belt has glazed the pulleys and made them too smooth, producing a slippery surface for the belt to run across. In this case, use a wire brush or steel wool to clean the surfaces of the pulleys the serpentine belt is wrapped around. After breaking up the glaze, apply brake cleaner or an industrial solvent to the pulleys. If you start the vehicle after applying brake cleaner, the motion of the belt will rub the glaze off the pulleys. The fan belt should now have more friction with which to turn.
In addition to a worn belt or glazed pulleys, other problems can cause a squealing belt. These problems include bad bearings in the belt tensioner or malfunctioning pulleys. The tensioner is responsible for keeping the belt tight. If the tensioner is slipping, the belt becomes too loose, creating a squealing noise. Malfunctioning pulleys may not turn properly or go out of alignment. This puts additional strain on the serpentine belt. If this is the case, the pulleys or the tensioner need to be replaced or aligned, usually by a trained auto mechanic.
If a squealing serpentine belt is not replaced, eventually it may snap. If this happens, the vehicle will stop functioning. The power steering will stop working and the water pump will no longer cool the engine. The alternator will not function, so the vehicle will not start. If your vehicle has a squealing belt, take your vehicle to a repair shop to have a mechanic diagnose and fix the problem.