The trend for motor oils has been steadily moving to lower viscosity oils for many years now. The use of 20W / 50 and 10W40 oils used to be the standard but these days both 5W / 30 and 5W / 20 have become common. Now we are seeing the use of 0W / 20 oils becoming prevalent, especially in highly fuel-efficient hybrid cars and trucks.
But what exactly do these numbers mean? When reading the information on a bottle of motor oil the top number indicates the oils viscosity. This is a measurement of how the oil flows at a given temperature measured in units called centiStokes (cSt). The bottom number with the "W" is its winter or cold weather rating and tells you how the oil flows at cold temperatures. The smaller the number in front of the "W the better the oil will flow when it is cold and the lower its point point generally is.
With the advent of EPA CAFE (corporate average fuel economy) requirements car makers started looking for any way possible to increase vehicle fuel economy. Since lower viscosity oils have inherently less drag and resistance to flow then heavier oils the trend had been lighter to more efficient oils. Lighter oils can significantly improve fuel economy, often by 2 to 3 miles per gallon compared to the old 40wt. and 50wt. oils once common and that's why we have seen the move to 20wt. Oils. Unfortunately, along with these early 20wt. Oils, came reduced wear protection.
One of the biggest problems related to the lighter viscosity oils being far more volatile. Many if not most early 5W / 20 and 0W / 20 petroleum motor oils were so volatile (meaning the lighter portions of the oil would boil off when the oil got hot leaving the heavier portions and causing the motor oil to thicken) that within one to two thousands of miles the oil had thickened into the 30wt. viscosity range. This reduced or eliminated any advantage in efficiency that had been gained by going to the lighter oil to begin with. Film strength of these lighter viscosity oil was also not as good and that wear protection was often very poor compared to higher viscosity motor oils.
With the advent of hybrid cars a few years ago 20wt. oil really started to come into its own. Today we are seeing more more use of synthetic and synthetic blend 20wt motor oils that offer all the protection once found in heavy viscosity motor oils Full synthetic motor oil has many times the film strength of a petroleum oil at any given viscosity. Also, synthetic oils with their uniform molecular structure are far less volatile and not near as likely to "cook" and change viscosity in the high temperatures of the modern pollution controlled engine. Full synthetic motor oils also flow far more readily and produce much less friction and drag inside of the engine and drive train than petroleum oils do and so lend themselves well to use in modern highly fuel efficient hybrid cars.
In 2008 Amsoil Inc. introduced ASM 0W / 20; an industry leading, high tech full synthetic motor oil made from advanced polyalphaolifin and synthetic ester base stocks combined with state of the art anti-wear additive chemistry. This cutting edge motor oil offers incredible wear protection and maximizes the inherent fuel efficiency of the modern hybrid car.
Since environmental consciousness and fuel saving is at the heart of hybrid car ownership for many individuals that purchase them, Amsoil ASM is also designed for one year or up to 25,000 mile drainage intervals. This vastly reduces the amount of motor oil that the car consumes and the amount of used oil that must be re-cycled. Having to purchase less oil changes through the course of the year also adds an element of convenience and savings to the ownership of these modern fuel-efficient marvels. Amsoil Inc. introduced the first full synthetic motor oil to meet American Petroleum Institute service requirements in 1972. Today Amsoil is considered the world leader in synthetic lubrication.