Serpentine Belt (Auxiliary Belt)

It is a ribbed belt that winds around several pulleys at the front of the engine. A spring tensioner keeps it tight. Some engines use a separate belt for each accessory instead of one long belt. Cracks across the ribs, missing chunks, glazing and fraying are signs that the belt should be replaced. Many belts are checked at every service.

The crankshaft pulley drives the belt, and the belt turns each accessory pulley. Friction between the ribs and the pulley grooves transfers the power.

A worn or loose belt squeals, especially at cold start or with the air conditioning on. If it breaks, the battery stops charging and, if it drives the water pump, the engine can overheat. Some cars use a stretch-fit belt without a tensioner, which needs a special tool to fit correctly.