Serpentine Belt Diagnosis
Today's automotive belts are made of neoprene or EPDM. EPDM belts last much longer because the material used in them has more elasticity. This additional elasticity makes them much less vulnerable to cracking. These belts squeal if there's not enough tension or if the belt is worn and stretched. It's best to use a belt wear gauge when considering the replacement of a belt.
A good belt rides a little above the pulley to allow dirt and debris a pathway out of the belt system. As the Neoprene or EPDM belt wears, the gap between the pulley and the ribbed belt begins to decrease. It rides deeper into the grooves and prevents dirt and debris from leaving the belt system. This is known as hydroplaning. It may not be noticeable because of the belt's ability to resist cracking.
A belt wear gauge is best for diagnosing most automotive belts. A loss of 5% of the belt's material results in a loss of belt performance. A belt wear gauge measures the depth of the belt. On a new EPDM serpentine belt, the gauge rises above the ribs. If the belt is worn, the gauge sinks into the belt, indicating the need for replacement.