The serpentine drive belt is what keeps your battery charged, your engine cool, steering easy to turn and keeps you cool when it's hot enough to fry bacon on the sidewalk. But how often do you really think about it? Not often enough I'll wager.

You are driving down the road and it's about 110 degrees and 95% humidity outside. But you don't care, the A/C is cranking out cold air by the ton and you are cool and dry. You pull onto the freeway and soon your cruising at 70 mph on your way home from work. All of a sudden the engine jerks and makes a loud screech. The battery light comes on and the A/C is not as cold as it was and getting warmer and the temperature gauge begins to climb. You find a safe to pull over and when you stop, there is steam pouring out from under the hood. You pop the hood and when the steam clears, you see pieces of fan belt all over the engine.

That Old Myth...

Just about every late model car and truck use a serpentine drive belt. It is a single ribbed belt that drives all the accessories, A/C, Power Steering, alternator and various other pumps and accessories. They should require no maintenance unlike their predecessors the V-Belt that needed periodic adjusting. But the fact of the matter is they don't last forever and they do need to be inspected often to keep you from getting stuck. If it starts to go bad, you can replace it at a time of your choosing and not when the belt decides for you. Checking ribbed drive belts at every oil change, and the position of the self-adjusting mechanism indicator, will insure you catch a bad belt long before it snaps.

The backside of the serpentine drive belt, or the smooth side, usually drives the water pump. If the serpentine belt gets oil soaked or glazed, it will slip and not provide the proper circulation to keep the engine cool. And if there is oil on the serpentine belt, it's coming from somewhere so you will need to find out where and fix it before putting on a new serpentine drive belt.

Look for tears or abrasions. If you see any it means the serpentine drive belt is rubbing a pulley flange or bolt as it winds it way around. This will happen more often as the drive belt gets older. If this happens you may need to file a pulley flange smooth or bend something out of the way.

Also look for pinholes and/or bumps. If you see any it means dirt and debris is getting in between the serpentine drive belt and the pulleys. Turn the belt around and see if there are chunks of the ribs missing. You can crank the engine to expose sections of belt as you inspect. A few, small widely spaced chunks are okay, But if there are many and/or close together, replace the serpentine drive belt. Hairline cracks are normal, but if they go into the backing, or flat side, of the serpentine drive belt you will need to replace it.

V-Ribbed Serpentine Drive Belt With Cracks Across Ribs

V-Ribbed Serpentine Drive Belt With Chunks of Rib Missing

A good rule of thumb for serpentine drive belts is that if cracks are observed 3 mm (1/8 in) apart, all around the belt, the belt may be reaching the end of its serviceable life and should be considered a candidate for changing. Small cracks spaced at greater intervals should not be considered as indicative that the belt needs changing. However, the onset of cracking typically signals that the belt is only about halfway through its usable life.