The serpentine belt (also called the drive belt or accessory belt) is a single continuous belt that drives multiple engine accessories including the alternator, power steering pump, air conditioning compressor, and sometimes the water pump. When it wears out or breaks, these systems stop working simultaneously. Replacing it is a straightforward DIY job that prevents a roadside breakdown.
When to Replace
Most serpentine belts last 60,000 to 100,000 km, but should be inspected regularly and replaced if they show cracking on the ribbed surface, fraying at the edges, glazing (a shiny, hardened surface), missing chunks, or squealing that does not resolve with adjustment. A belt that breaks while driving will cause immediate loss of power steering, charging, and air conditioning, and on vehicles where the belt drives the water pump, rapid engine overheating.
How the Belt System Works
The belt wraps around the crankshaft pulley (which drives it) and routes through a series of accessory pulleys. An automatic tensioner with a spring-loaded arm maintains the correct belt tension. The belt routing is specific to each engine – even different engine options within the same vehicle model can have different routing patterns. Your workshop manual includes a belt routing diagram showing exactly how the belt wraps around each pulley, which is essential for correct installation.
Replacement Procedure
Before removing the old belt, draw or photograph the routing. Even with a diagram, having your own reference of the installed belt prevents confusion during reassembly. Locate the automatic tensioner and use a socket, spanner, or dedicated belt tool to rotate it and release tension on the belt. Slip the belt off one pulley while holding the tensioner back, then release the tensioner and remove the belt completely.
While the belt is off, spin each accessory pulley by hand and the tensioner pulley. They should spin smoothly and quietly. Any grinding, roughness, or wobble indicates a worn bearing that should be replaced before fitting the new belt. A failing idler or tensioner pulley will destroy a new belt quickly.
Route the new belt according to the diagram, leaving one pulley for last. Rotate the tensioner again, slip the belt onto the final pulley, and slowly release the tensioner. Verify the belt is seated correctly in the grooves of every pulley. Start the engine and observe the belt running for a few seconds to confirm it tracks correctly without wandering off any pulley.
When to Replace the Tensioner
The automatic belt tensioner has a limited lifespan and should be replaced if it no longer holds adequate tension, if the tensioner arm oscillates visibly while the engine runs, or if the tensioner pulley bearing is noisy. Many mechanics replace the tensioner and idler pulleys at the same time as the belt as preventative maintenance, since the labour is the same.
Your Manual Has the Details
Belt routing, tensioner bolt sizes, and the correct belt part number are engine-specific. Your workshop manual provides all of these. MechanicMate offers PDF workshop manuals for over 960 vehicle models at mechanicmate.net/shop.
