We’ve all looked at a container of oil at one time or another and wondered what everything on its label meant, or even if the oil we’re using is the best grade for the job. But by the time you get home from the auto-parts store, your mind is probably focused on more important things, and you don’t think about it again until it’s time for another oil
change. But motor oil is an interesting, sometimes complex subject that deserves your attention – and if what you’ve wanted is someone to break it down for you in laymen’s terms, this story is for you.
Read the Label
Just about everything you need to know about oil is on the American Petroleum Institute (API) “donut” on the back of the bottle – that is, if you know how to decipher its meanings. At the top, you’ll see the words “API Service,” followed by two or more letters. Designations beginning with the letter S (such as SM, SL, SJ) are service categories designed for gasoline-burning, or S for spark ignition, engines. Those beginning with C (such as CJ-4, CI-4, CH-4 and CG-4) are commercial categories designed for diesel, or C for compression ignition, applications. See the sidebar on page 40 for an explanation of these codes.
In the center of the donut are the numbers that will most likely concern you; these numbers indicate the viscosity grade of the oil. Put simply, viscosity is a measure of an oil’s thickness typically expressed in numbered grades ranging from 5 (thinnest) to 50 (thickest). Established by the Society of Automotive Engineers, (SAE) an oil’s viscosity was originally a single grade, or “straight weight,” but that changed when the SAE added winter grade-designations, indicated by a “W” after the viscosity grade (i.e. 10W). Engineers realized that the existing grade specification did not adequately identify the
cold-weather characteristics of a particular oil; depending on what region the crude came from (the United States or Persian Gulf, for example), two oils with the same grade could exhibit very different viscosities.
The evolution of motor oil took another big step a short time later, when advances in petrochemical engineering led to the development of viscosity enhancers that made it possible for a single oil to serve double duty in both low and high temperatures. These became known as “multigrade” oils, and are the ones we are familiar with today. These oils from brands such as Royal Purple, Shell Rotella T, Amsoil and Chevron flow a like lower-viscosity oil to make it possible for oil to flow easily to critical engine components in freezing temperatures, but then protect like a heavier weight oil at the SAE-specified 210° F. Hence the oils we’re all familiar with: 10W-30, 10W-40, etc.
Today’s engines are assembled with greater precision and have tighter tolerances than the engines of yesteryear, which is why 5W-30 is the most common automotive oil grade for gasoline engines, 15W-40 for diesels. Typically, it is recommended that you stick with the oil grade recommended by the manufacturer, but this is not always the case. Bear in mind that the manufacturer’s recommendation is based on a new or as-new engine operated in a typical environment; a high-mileage engine, or one operated in extreme heat or cold may be better suited to a different oil grade. Moreover, oils have a temperature operating range, so if you’re in a jam and need to add a quart or two of oil to your engine, but your grade isn’t available, you’ll be fine to select a different grade. For example, the API cites 5W-20, 5W-30, 10W-30, 10W-40 and 20W-50 as being suitable for passenger cars operated at temperatures no lower than 32° F.
Oils designated for gasoline-burning passenger cars and light trucks will have “Energy Conserving” displayed at the bottom of the donut, indicating that the oil has been formulated to conserve fuel. For diesel applications, you will find the CI-4 PLUS designation. Used in conjunction with API CI-4 and CJ-4, the CI-4 PLUS designation identifies oils formulated to provide a higher level of protection against soot-related viscosity increase and loss in diesel engines. Elsewhere on the label, you may find reference to “ILSAC,” which means that the oil meets the current engine protection and fuel-economy standards of the International Lubricant Standardization and Approval Committee, a joint effort of U.S. and Japanese automobile manufacturers.
Though synthetic oils were introduced to the mainstream consumer market decades ago, there still exists an abundance of uncertainty, misinformation and outright falsehoods on the subject. First off, synthetic oil isn’t really synthetic – it still uses a petroleum “base stock,” which is transformed using a process known as organic synthesis.
When oil is pumped out of the ground, it has hydrocarbon chain links of all sizes, which create two issues. One, the chains have gaps which allow oxidation and breakdown to occur. Two, the lighter molecules will eventually boil off, leaving the heavier molecules behind. This not only changes the viscosity of the oil, it also leads to sludge and varnish build-up.
When the petroleum-oil base stock undergoes organic synthesis, however, uniform molecular structure is achieved, and a “perfect” oil is created. This offers a number of benefits, including greater film strength (for better wear protection), a lower pour point (for easier pumping in cold weather) and greater lubricity, which can result in reduced operating temperature, improved fuel economy and more power. And as we mentioned earlier, synthetic oils are less volatile and therefore not prone to “boil off” like traditional petroleum-based oils are.
It is a commonly held belief that synthetic oils should not be used in a new engine, but many high-performance vehicles such as the Corvette and Viper come from the factory filled with synthetic oil, as do many European imports. There has also been some concern that synthetic oils can cause oil leaks in older engines, as the higher detergent qualities of
synthetic can wash away varnish that keeps gaskets sealed. This can, in fact, take place – but it depends largely on the engine, its mileage and overall condition.
Oil-change intervals have historically been another topic of debate, but realistically, how often you change your oil has a lot to do with the age of your vehicle and the way you drive (mostly city, or mostly highway). Years ago, presiding engine technologies mandated that oil be changed around every 3,000 miles or so, but that’s not the case today. Recall
that most engines from the mid 1980s and earlier had less-evolved fuel and ignition systems, so the oil got dirtier and/or contaminated more quickly.
Today’s engines can often go 7,000-10,000 miles before a change is needed, again, depending on how the vehicle is driven (see your owner’s manual for the recommended change interval). Proof of this can be found in the oil life systems used by some newer vehicles. These systems assess exactly when the oil should be changed based on climate conditions and how you have used the vehicle. General Motors estimates that its vehicles’ systems allow its customers to go from five oil changes a year to only two or three. From a cost standpoint the 3,000-mile oil change interval is still a lot cheaper than an engine rebuild, and it certainly won’t harm anything.
Synthetic oils, such as those offered by Amsoil, Bardahl and Shell Rotella T, can go even longer between oil changes, because they don’t break down and become sludgy. In fact, some synthetic motor oils have a recommended change interval of 25,000 miles or one year; you simply replace the filter after six months, and top it off with more oil. But a
change eventually becomes necessary because, although the oil itself doesn’t break down, its detergents and additives eventually will. If in doubt, you can always send out a sample of your engine’s oil for analysis to determine its condition. Several synthetic oil companies offer this service, as do many other companies you can find on the Internet by typing in the words, “engine-oil analysis” in your search engine.
If you omit the technical details of refining and testing, understanding today’s engine oils isn’t difficult. Use the recommended oil for your application, keep the fill level up and change it when necessary, and motor oil will serve you (and your engine) well for many years to come.
Amsoil, (715) 399-8324, www.amsoil.com.
Bardahl, (206) 783-4851, www.bardahl.com.
Castrol USA, BP Lubricants USA Inc., (800) 462-0835, www.castrol.com.
Chevron, (800) 582-3835, www.chevron.com.
Exxon Mobil Corporation, (800) 662-4525, www.mobiloil.com.
Pennzoil, (800) 332-6457, www.pennzoil.com.
Quaker State, (800) 237-8645, www.quakerstate.com.
Red Line Synthetic Oil, (800) 624-7958, www.redlineoil.com.
Royal Purple, (888) 382-6300, www.royalpurple.com.
Shell Rotella, (800) 237-8645, www.shell.com.
Valvoline, (800) 832-6825, www.valvoline.com.