How Often Should Belts and Hoses Be Replaced?

Most hose manufacturers recommend replacing hoses every four years.   Belts should be replaced every three years or 36,000 miles.  The incidence of failure rises sharply after the fourth year of service for hoses and third year for belts.  The life span of a typical serpentine belt is about five years or 50,000 miles.  Serpentine belts are thinner and more flexible than V-belts.  They run cooler and last longer, but cost about twice as much to replace.  The hard part is convincing customers to change belts and hoses as preventative maintenance BEFORE they fail.  Few people do, yet they could save themselves a lot of unnecessary grief and expense if they would.

Rubber hoses deteriorate with age.  Tiny cracks develop in the rubber which eventually cause hoses to split, blister, or leak.  Oil contamination and atmospheric ozone can accelerate the process.  Engine vibration and motion can cause hoses to wear if they are too short or rub against other parts.  This applies to fuel, vacuum, and emission hoses as well as coolant hoses. 
A visual inspection will often uncover bad hoses.  Pinching hoses to check for age cracks, brittleness, or mushiness can also help locate hoses that need to be changed.   However, neither technique will reveal all the hoses that might need replacing because hoses wear as much from the inside out as they do from the outside in.  A hose that appears okay on the outside may actually be on the verge of failure because of internal deterioration.

According to research done by one hose manufacturer, internal corrosion caused by electrochemical degradation is the primary cause of cooling system hose failure.  The coolant acts like an electrolyte and allows a current to flow between engine and radiator.  This causes micro-cracks to form inside the hose which eventually leads to pinhole leaks and weakening of hose fibers. 

With belts, heat, and mileage are the main causes of wear.  Every time a belt passes around a pulley, it bends and flexes.  This produces heat which hardens the rubber over time.  The wear process is greatly accelerated if the belt is loose and slips.

The additional friction between belt and pulley will make a belt run hotter.  After millions of journeys around the pulleys, even the best drive belt begins to suffer the effects of age.  Rubber begins to crack and fray and the internal cords become weak and brittle.  You cannot always determine a belt's true condition by appearances alone.  Any belt obviously cracked and frayed should be replaced.  With many of today's bandless belts, there is no outside cover to peel loose and betray the belt's deteriorated condition.

When a belt is replaced, it is important that the belt be properly tensioned.  If too loose, it will slip and wear quickly.  If too tight, it may damage internal cords as well as overload shaft bearings on accessories it drives.

The rule of thumb about tightening a belt until there is about half an inch of give between the two furthest pulleys is not always accurate.  A belt gauge that measures actual tension is the only sure way to know if a belt is tensioned properly.

Because a V-belt normally takes a set after a few minutes of running, one set of tension specs may be provided for new belts and another for used belts.  Any V-belt that has been run for more than 15 minutes should be considered a used belt.