Motor oil: it's all too easy to use the wrong one
Jacques Gordon
Watch a race on television and you'll see motor oil commercials that tell you their brands offer the best protection for your engine. The fact is, all motor oil brands approved for use in street engines must meet the same minimum performance standards, and today, it's the original equipment manufacturers that set those standards. So for technicians or do-it-yourselfers, it's easy to buy a good brand of motor oil, but there are important differences in the types or grades of oil that make it all too easy to buy the wrong one.
No matter what brand is used, there are a lot of decisions to make when selecting oil for a given engine. Deciding incorrectly can be costly, as Mercedes-Benz owners across the United States recently found out when regular motor oil was used in engines that were supposed to be filled with synthetic oil. Choosing between petroleum and synthetic oil is only one of several decisions. The only way to know for sure that the right oil is being used in any given engine is to check the specifications in the owner's manual, service manual or another trusted source.
In addition to viscosity specifications, which are now more important than ever, a customer has to select the right American Petroleum Institute (API) service category. Most service manuals specify motor oil with the API "starburst" symbol, certifying that the oil meets all the needs of a light-duty automotive gasoline engine. However, they've recently called for motor oil that conforms to a specific service category, too.
What's a service category?
A service category certifies the oil's ability to pass specific lab tests that measure the oil's ability to perform in an engine. Oil is tested for the way it pours when hot or cold, its ability to resist wear, foaming, oxidation and deposit formation at various temperatures and several other physical and chemical qualities. It is tested when new, and again after being run in an engine. Many of the certification tests are bench tests, and for these, the engine is used only to "age" the oil. Still, oil that can pass all the tests will perform predictably in a real-world engine.
API licenses two different certification labels to oil marketers--the brand names we all know. The specifications for one of those labels are generated by the International Lubricant Standardization and Approval Committee (ILSAC), a group consisting of the Big Three domestic car manufacturers and the Japanese car manufacturers. ILSAC defines the performance characteristics and the chemistry of the oil it will accept for use in its engines, and API makes sure the oil sold by marketers displaying that label meets that definition. Some oils meet both the API service category and the ILSAC specifications; these will carry both labels.
There is another group of service ratings generated by European carmakers under the ACEA, which translates from French to English as the European Automobile Manufacturers Association. Many ACEA specifications are based on the same American Society for Testing and Materials (ASTM) tests used by API. So far, the ACEA service ratings rarely appear on oil containers sold in the United States. While things may change in the future, the service categories based on ILSAC specifications are officially considered "close enough" for European cars sold in the United States.
Oil design committee
Motor oil has become a very sophisticated fluid that's designed by committee. Those committee members come from four different groups: automakers, oil marketers, chemical companies and automotive engineers.
The Society of Automotive Engineers (SAE) is an international group of engineers working in different companies in all areas of transportation, not just automotive. Their goal is to create a standard language and definitions to ensure a given thread pitch, oil viscosity or diagnostic trouble code will be the same in Detroit, Stuttgart and Tokyo. Most people are familiar with the SAE viscosity numbers on a bottle of oil, even if they don't know exactly what those numbers mean.
The API represents the oil marketers. Like SAE, the API creates industry standards that define equipment, practices and products, and those standards are applied from the wellhead to the end user. Operating since 1924, the API service categories have been on oil bottles for decades. They've changed many times in recent years, mostly due to changes in engine and emission control technologies.
Working closely with all the other groups involved, the chemical companies that make the oil additives also participate in service category development.
As noted earlier, the automakers are represented by ILSAC, which was created in 1992. Issues surrounding operating temperature, forced induction vs. natural aspiration, extended oil change intervals and the ever-present need to improve emissions and fuel economy all began taking on more importance in the 1980s. API standards have always been applied to multigrade and single-grade lubricating oils used in a wide range of applications, but the automakers needed greater focus on developing oils and additives in the automotive grades. Since its creation, ILSAC has played a major role in defining automotive-grade motor oils.
Whether you buy motor oil by the quart, gallon or drum, somewhere on the label will be the words "API Services" followed by one or two pairs of letters. It may appear somewhere on the label as text, but it also must appear in what is commonly called the API donut symbol. These letters indicate which test series the oil has passed, which represents its impact on fuel economy and, in recent years, its compatibility with the engine's emissions control system. Oil that meets the ILSAC specs also carries the API starburst symbol.
Understanding the changes
Like so many other automotive technologies, motor oil has been redesigned several times to help vehicles meet ever-tightening emissions and fuel economy requirements. So far, chemists have been able to create oil for new engines that also satisfies all the needs of earlier engines, meaning it can be used with the latest service category rating in any automobile engine. However, right now, oils with earlier service category specifications are still available. This is why you should reinforce with your professional and DIY customers that they check the specs and the label before pouring. It's too easy to make a mistake.
Starting with the 2004 model year, the federal government requires auto manufacturers to cover catalytic converters under warranty for 120,000 miles. The active ingredients in a catalytic converter are platinum, rhodium and palladium, and they are very expensive metals. Over the years, engineers have been successful at reducing the amount of platinum-group metal needed to make a catalytic converter perform for extended periods. Most catalysts eventually fail because of poisons in the engine-out exhaust gas, and two of those poisons, phosphorous and sulfur, are in motor oil. Even new engines consume some oil through the crankcase ventilation system, and while it's a very small amount, it's unlikely these low metal-loading catalysts will meet the new 120,000-mile warranty requirement on engines using earlier service category oils. Rather than increase the metal loading--and, therefore, the cost--of new catalytic converters, the automakers decided it was time to change the chemistry of motor oil.
Producing low-phosphorus motor oil presents a problem because a particular zinc-phosphorus compound has been used successfully for years as an anti-wear agent. As a substitute, chemists developed enhanced friction modifiers for the additive package that also help improve fuel economy. So far the only real problem this has caused is in motorcycles that use a wet clutch. This is one reason why the earlier-spec catalyst-damaging oil is still being produced.
Producing low-sulfur motor oil requires a different base stock, which is the oil from the refinery that makes up more than 80 percent of a quart of motor oil. It's still made from organic crude, but with a different refining process. This has caused some temporary cost and availability problems, but it has also provided real advantages. The new base stock oil improves the finished product's cold-start performance and decreases its volatility, meaning a healthy engine will "breathe" less oil vapor.
The meaning of flow
Viscosity is a measure of the oil's ability to flow at a given temperature, which indicates how thick the oil film will be on metal parts. Obviously it flows more slowly and forms a thicker film when it's cold; a thinner film is formed when it's hot. Because automotive engines operate over a very wide temperature range, they use multi-viscosity oil that doesn't get quite as thin when hot or quite as thick when it is cold.
The Society of Automotive Engineers (SAE) is the keeper of viscosity specifications. When SAE 10W-30 oil is cold, it will flow like 10-weight oil does in winter temperatures (thus, the "W"), and like 30-weight oil when it's hot. This doesn't mean that multigrade oil gets thicker as it gets hotter; it means the oil flows the same as straight 30-weight oil does when it gets hot. multi-viscosity oil is created by adding polymers to narrow the change in flow-rate over wide temperature ranges.
In the ongoing effort to improve fuel economy, car manufacturers are designing their engines to use lighter oil, typically 5W-20 or 5W-30. Some of the hybrid engines are using 0W-20 oil. In any engine, oil has several functions, which include:
* Lubricating moving parts.
* Carrying heat away from engine parts.
* Acting as hydraulic fluid for lifters, tensioners and actuators.
* Sealing the rings to the pistons and cylinder walls.
Today's engines are tighter and built with greater precision, so low-viscosity oil is quite adequate for these tasks. It improves fuel economy because it's easier to pump, which reduces engine power needed for the oil pump (parasitic loss) and creates less drag on rotating parts (windage loss). Once the engine is warmed up, using oil that's one or two grades thicker usually doesn't cause any problems other than reduced fuel economy. However, when it's cold, thicker oil flows slower, which can cause damaging wear during cold-start and, under certain conditions, can also prevent hydraulic lifters and tensioners from bleeding down as designed.
So what's the right oil?
There are two different sets of service categories, one for gasoline engines and one for diesel engines. Gasoline oils are all in the "S" category, and diesel oils are all in the "C" category. The issues described in this article apply only to automobile gasoline engines. The categories have been updated as needed, and since the creation of ILSAC in 1992, there have been five new categories for gasoline engines. With each update, the second letter in the service category advances in the alphabet, so SF oil is newer than SE oil.
The newest API service category for gasoline engines is SM. The API donut on the label will also include the words "energy conserving" since the oil is designed to improve fuel mileage. While the actual improvement may be marginal on any given vehicle, the fuel savings will add up nationally as the whole fleet gradually changes over to energy conserving oil.
Some marketers have been making the earlier SL category oil with the new low-sulfur, low-phosphorus base stock, but only the SM service rating has both the base stock and additives that conform to the latest ILSAC GF-4 specifications.
Although the extended catalyst warranty was required for the 2004 model year, the GF-4 specifications weren't finalized and released until January of that year. That is well into the production cycle for that model year, so many cars left the factory with the older-spec oil. In addition, production of SL (ILSAC GF-3) oil will continue at least until April. Because the newer oil isn't suitable for wet-clutch applications, older oils are likely to remain in production. That means you are likely to still find SL and even SJ oil on the parts shelf for some time to come.
The oldest service category still considered current is SJ, which conforms to ILSAC GF-2 specifications. According to API, it is still suitable for 2001 and earlier model-year engines and may still be available. Earlier service category oils (SH and back) are considered obsolete, so it is less likely you'll find anyone requesting them. However, they all still meet the needs of engines they were designed for, so don't be afraid if a tech or DIYer calls for new/old stocks of oil, just ask what engine it is for.
When it was common practice to change oil every 3,000 miles, almost any readily available automotive oil would do. This is no longer true. Today, only oil of the right viscosity and API service category or ILSAC spec are likely to get an engine and its catalytic converter through the warranty period, especially for vehicles built for the 2004 and later model years. All oil approved for automotive use will display the oil's specifications on the container, and many vehicles now have the service manual's oil specifications printed on the filler cap.
Thanks to all who provided information for this article, including ConocoPhillips, Chevron, procarcare.com, Quaker State and Kevin Ferrick, API's engine oil program manager.
OIL LABELS IN ACTION
The API starburst indicates the oil has been approved for use in automotive gasoline engines. It's surprising how easy it is to find oil that's not approved. The API label on the back shows everything you need to know about the oil in the bottle. The API service category letters (SM) should match or supercede those called for in the vehicle's service specs. The SAE viscosity rating is in the center, and "energy conserving" shows the oil meets ILSAC's latest specifications. Some vehicles have these requirements printed on the oil filler cap.
COPYRIGHT 2005 Advanstar Communications, Inc.COPYRIGHT 2005 Gale Group
