There’s a lot to know about the oil you put in your engine, but learning about designations, viscosities and change intervals isn’t difficult and can net longer service life

By Chris Hemer

rowing up, changing one’s own oil was a rite of passage. Sure, you could take it to the dealership or a local mechanic to have the job done, but if you were a real car (or truck) fanatic, you proved your devotion to the machinery by doing the job yourself. In fact, if you’re like many of us on this very magazine, you’ve probably opened hundreds of quarts of oil over the years — you might even remember spearing a metal-topped can with an oil spout. But do you know what all those numbers, letters and symbols on the bottle mean? How about the differences between standard and synthetic oils, or when they should be changed?

If not, don’t worry — you’re not alone. But, if you are a dedicated car/truck/RV nerd, you should learn, because the science and technology behind contemporary oil formulations continues to change — and is actually pretty interesting stuff when you break it all down. Plus, understanding oils can help you get the most out of your engine in the long run.

Letters and Numbers
The American Petroleum Institute (API) is the organization that represents all segments of America’s oil and natural gas industry, and since its inception in 1919 it has developed more than 700 standards to enhance operational and environmental safety, efficiency and sustainability. The API’s Engine Oil Licensing and Certification System (EOLCS) is a voluntary licensing and certification program that authorizes engine oil marketers who meet specified requirements to use the API Engine Oil Quality Marks. These emblems go directly on each container of oil that retains the certification(s) and are there to help consumers identify quality engine oils for their gasoline-and diesel-powered vehicles.

The API SP designation was introduced in May of last year. It offers improved fuel economy for newer engines and protection for the emissions control system as well as for engines running on fuels containing ethanol up to E85.

Just about everything you need to know about an oil is on the API “donut” on the back of the bottle. For example, at the top of the donut, you’ll see the words “API Service”, followed by two or more letters. Letters beginning with the letter S (such as SN, SM, SL, SJ) are service categories designed for gasoline-burning engines. Letters beginning with C (such as CK-4 CJ-4, CI-4 and CH-4) are commercial categories designed for diesel applications. (See the sidebar for an explanation of these codes and what they mean.)

In the center of the donut are the numbers that you’re most likely concerned with, which indicate the viscosity grade of the oil. Put simply, viscosity is a measure of an oil’s thickness — its ability to flow at certain temperatures — typically expressed in numbered grades ranging from 0 (thinnest) to 50 (thickest). Originally established by the Society of Automotive Engineers, (SAE) an oil’s viscosity was once 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 single-grade specification did not adequately identify the cold weather characteristics of a particular oil. For example, depending on the region the crude came from, two oils with the same grade could exhibit different viscosities.

The evolution of motor oil took another big step when advances in petrochemical engineering led to the development of viscosity enhancers, which made it possible for a single oil to serve double-duty in both low and high temperatures. These became known as “multi-grade” oils and are the ones we utilize today. These oils flow like a lower-viscosity oil in freezing temperatures but protect like a heavier-weight oil at higher temperatures. Hence the oils we’re all familiar with: 10W-30, 10W-40, etc.

5W-30 grade oil, like this Valvoline, is the most popular viscosity for today’s gasoline engines. The High Mileage Maxlife is a synthetic blend designed to maximize the life of engines with 75,000 miles or more.

Today’s engines are assembled with greater precision and have tighter tolerances than their predecessors, which is why 5W-30 is the most common automotive oil grade for gasoline engines; 15W-40 for diesels. Generally speaking, it is recommended that you stick with the oil grade recommended by the manufacturer — but not always. 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, 10W-30 or 10W-40 instead of 5W-30). In fact, there are some oils designed for diesel engine service that might also meet gasoline engine service standards. These “multiple performance level” oils can be identified by the “C” category first, followed by the “S” category (example: “API Service CJ-4, CI-4/SN”).

Oils designed for gasoline-burning passenger cars, vans and light trucks will have the terms “Energy Conserving” or “Resource 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. This designation identifies oils formulated to provide a higher level of protection against soot-related viscosity increases and losses 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.

Synthetic Oils
Regardless of what its designation suggests, synthetic oil isn’t truly synthetic — it still uses a petroleum “base stock” (rather than whole crude oil), 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 for a vehicle engine application. 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, but it also leads to sludge and varnish build-up.

Mobil was the first company to put synthetic oil in the mainstream. The company now offers a variety of full-synthetic products, including this 5W-30 formulated for truck and SUV applications.

When the petroleum oil base stock undergoes organic synthesis, however, uniform molecular structure is achieved. 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 translate into reduced friction, 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. It is a commonly held belief that synthetic oils should not be used in a new engine, but many high-performance and hybrid vehicles have come with a factory synthetic oil fill for a decade or more. In fact, synthetic oil use is becoming more commonplace in all types of vehicles, as it has been shown to improve fuel efficiency and provide better protection than ordinary engine oil. Conversely, some have cautioned against using synthetics in older, high-mileage engines, as the higher detergent qualities of synthetic can wash away varnish that keeps gaskets sealed — which means new leaks. Though this is a possibility, it depends on the engine, its mileage and overall condition.

Change Intervals
Oil change intervals have historically been another topic of debate. Realistically, how often you change the oil has a lot to do with the age of the vehicle and the way you drive (mostly city, mostly highway, heavy towing, dirty/dusty conditions, etc). Years ago, prevailing engine technologies (and marketing campaigns by oil-change franchises) suggested that oil be changed around every 3,000 miles or so, but that’s no longer the case. Remember that most gasoline engines from the mid ’80s and earlier did not benefit from efficient electronic fuel injection or coil-on-plug ignition, so the oil became contaminated much more quickly. Today’s gasoline engines can often go 7,000-10,000 miles with ordinary (non-synthetic) oil before a change is needed — again, depending on how the vehicle is driven.

To make things easier on the consumer, so-called “oil life monitoring” systems were introduced in the late ’80s. These systems collect data such as idle and drive time, average engine temperature, load and other information, which is then run through a mathematical algorithm that predicts when the engine oil will begin to break down, usually in the 5,000-8,000 mile range. It’s important to note here that oil life monitors don’t monitor oil condition — so while most peoples’ driving habits may be normal, heavy-duty RV service dictates shorter intervals, as does driving in extremely dirty or dusty conditions. Always consult the owner’s manual or service center for advice on oil change intervals if you think your application is outside the norm.

Synthetic oils can go 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 up to 25,000 miles or one year (whichever comes first). However, 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; some 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 of choice.

Engine oil is something many of us tend to take for granted. But understanding its application and maintaining the recommended change intervals are key to a long service life for your tow vehicle or motorhome.

Sources:

American Petroleum Institute (API)
api.org

SAE International (formerly Society of Automotive Engineers)
sae.org

AMSOIL
(800) 777-7094
amsoil.com