Alternator Pulley

WHAT IS A PULLEY?        WHAT DOES A PULLEY DO?

Pulleys are simply a means of  transferring power.  In the automotive pulley and belt system the power generated by the engine is transferred from the Engine Crankshaft  pulley to the belt and then from the belt to the pulleys attached to various accessories such as the Alternator, Power Steering Pump, Air Conditioning Compressor, Water Pump etc.  In the early years of automobiles a narrow "V' shaped belt was used to drive the accessory pulleys with vehicles having as many as 3 separate belts.   Most modern vehicles use only one belt to drive all the accessory pulleys. This is a wide belt that is flat on one side and has small "V" shaped ribs on the other side. Both the flat (smooth) side of the belt and the ribbed side can be used to drive pulleys. This belt is commonly referred to as a serpentine belt but also goes by many other names including Multi-V belt, Poly-V belt, Poly-Ribbed belt, Micro-V belt and others. Depending on the vehicle and engine the number of "ribs" made into the belt , which determines the width of the belt, varies from 5 to 8 with 6 being by far the most popular size or width. Alternator pulleys also come in various outer diameters.

CLUTCH PULLEYS AND DECOUPLER PULLEYS
Although the pulleys used from the earliest days of the automotive era were trouble free and nearly fail proof, unless not secured properly, starting around 1997 the powers that be saw fit to change all that. First came the Overrunning Alternator Pulley (O.A.P.) also known as a One Way Clutch type pulley(O.W.C.). Then a few years later the Overrunning Alternator Decoupler type pulley (O.A.D.) was introduced. Typically three reasons are given for the introduction of these new more complex pulleys.
The reduction of the mechanical load (drag) on the entire belt system which reduces the vibration in the belt drive system and decreases belt tensioner motion.
That it increases the expected life span of ALL the components driven by the belt due to the positive effects of reason #1.
Incresed fuel economy due to the positive effects of reason #1.

I have no doubt that the engineers at both the pulley manufacturer and the car makers have piles (or the digital equivalent of a piles) of technical research and data to back up these claims but permit me to make three counter points based on 30 years of rebuilding experience.
#1... The simple solid type pulleys used in the past which were made from stamped steel or cut from  cold rolled steel had an average life span of infinity when properly installed and not damaged due to a car crash or some other damage. The expected life span of a decoupler type pulley, according to the website of the company that manufactures them, is 40,000 to 60,000 miles. I am almost certain that infinity is greater than 60,000 so the life span of the alternator at least is NOT increased.
#2... According to the website of the company that manufactures decoupler type pulleys the total global vehicle fleet with their pulley installed is 20 million. According to the website Statistic Brain the total global fleet of passenger cars produced from 1999 to 2013 is 745,568,010. If my math is right that's between 2%-3% coverage.  (  If you were to  Include commercial vehicles produced during that time it would make that percentage even lower.)  If these pulleys were the miracle cure all claimed why such limited adoption by car manufacturers?
#3... According to the decoupler type pulley manufacturers website the fuel efficiency gains achieved by their product is from 1%-2%.  According to Fuel Economy Website for the federal government (fueleconomy.gov) the fuel effeciency gain of having properly inflated tires on a car is as much as 3.3% and the average fuel efficiency gain of having a properly tuned engine in  your car is 4% and the fuel efficiency gains from using the proper weight motor oil in your car is between 1%-2%. Heck, if you did all those things and waxed your car just right and ran with the windows up and the a/c off  your car might actually produce gasoline instead of consuming it.