Most hose manufacturers recommend replacing hoses every four years. With V-belts, every three years or 36,000 miles. The incidence of failure rises sharply after the forth year for hoses and third year for belts. A typical serpentine belt lifespan 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 they cost about twice as much to replace.