Most
late-model engines have serpentine belt drives for the engine-driven
accessories. But many don’t know the spring-loaded automatic tensioner
that keeps a serpentine belt tight is also a wear item.
The
automatic tensioner has a coil spring inside that applies just the
right amount of force against the belt to keep it tight. The tensioner
also provides a little “give” so it can absorb and cushion shock loads
on the belt that occur when the A/C compressor clutch cycles on and
off. What’s more, the tensioner automatically compensates for wear and
keeps the belt under constant tension.
The typical service life of a
serpentine belt is about 60,000 miles or five years. When the belt
nears the end of its life, it may become cracked, glazed and noisy.
If
an aging belt is not replaced, it may break, causing a loss of drive
torque to all of the engine’s accessories. All too often, an old
serpentine belt (or a broken belt) will be replaced with a new one. But
the automatic tensioner is not inspected to make sure it is still
working properly and is in good condition. Belt tension is critical.
Too little tension may allow the belt to slip and squeal. Slippage also
causes the belt to run hot and age prematurely. And if the belt is
really loose, it may come off its pulleys. Too much tension on a belt
may overload it as well as the shaft bearings on the water pump,
alternator, power steering pump and air conditioning compressor,
possibly leading to premature failures in these components.
The tensioner should always be inspected when changing a belt because:
• Rust or corrosion can jam the tensioner housing and prevent it from rotating freely.
• Dirt or mud can also jam the tensioner housing.
• A loose or worn pivot arm can allow unwanted movement that results in belt noise and misalignment.
• A worn bushing in the tensioner pulley can cause vibrations and noise. If the bushing seizes, it may cause the belt to snap.
•
A weak or broken spring inside the tensioner can’t maintain proper
tension and the belt will slip. Springs lose tension over time from
exposure to heat.
• Cracks or damage to the tensioner housing or
pulley arm may prevent it from rotating smoothly and maintaining proper
belt tension.