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The importance of using the correct engine oil.


Misunderstanding, misinterpretation, and some downright myths surround motor oil. This is largely because motor oil is an extremely complex, heavily researched, continuously improved and extensively tested product. However, it all looks, feels, smells and, we assume, tastes pretty much the same. While most humans can’t tell the difference, engines can.

Little has created more motor oil misunderstanding than synthetic oil. One reason: Unless you’re currently receiving an “A” in Advanced Placement Chemistry, the concept of making motor oil from something that is not oil is difficult to grasp.

Also, synthetic oil has radically evolved since it was first mass-produced during World War II by Germany, which had little petroleum but plenty of coal and methane gas. Soon after the war, chemists found that they could use other source material—such as ethylene gas—to create oil that would better survive the rigors of jet aircraft engines than that refined from crude oil. Called polyalphaolifin or PAO, these synthetics perform better in extreme conditions because chemists can design the oil molecules for the specific task and make all the molecules uniform. (Sign up for AP Chem if you want more.)

Synthetic oil can be made—synthesized—from many sources, including crude oil. If you see a couple guys in white lab coats wrestling on the ground, they’re probably oil-company chemists arguing the pros and cons of crude-oil-based synthetics versus PAO synthetics.

Here are some of motor oil fallacies that may, or may not, have been true in 1942 or 1982, along with the current truth.


It’s bad for my engine to switch between synthetic and conventional motor oil.


Today’s synthetics are totally compatible with conventional oil, and other leading synthetics. Switch back and forth all you want. Some who live where temperatures plummet well below zero use synthetic in the winter for its protection during cold starts and extreme temperatures and then switch to lower-priced conventional oil for warmer weather.


Synthetics are bad for engine seals.


Today’s synthetics are designed to play nice with all engine seals. While 30 years ago some synthetics reacted differently with some engine seals than did conventional motor oil, chemists for oil companies long ago cured that issue.


For the average motorist, synthetic has no significant advantage over conventional motor oils.


The top attribute of synthetic motor oil is its superiority in extreme conditions and one of the most severe is a “cold start”. Anything under 160 degrees or so is chilly to an engine.


Conventional motor oil is a natural and unprocessed product, while synthetic is made in a laboratory.


Both conventional and synthetic motor oils go through elaborate production processes: Oil straight from the ground would quickly ruin your engine. Base sources for synthetic oil are just as “natural” as is crude oil—and might even be crude oil.


Synthetic—or any other—oil can significantly improve horsepower.


Well this one really depends on you interpret the question and how you define significant. Let’s first look at whether or not switching from one oil to another can immediately give you more horsepower; for a race driver where a few tenths of a percent extra horsepower can be the difference between 1st and 5th the answer is yes but for a regular driver even one towing a loaded trailer uphill, the answer is no. Formulators can modify the frictional characteristics of an oil to allow more of the engine’s power to end up at the wheels, but these differences are too small to be seen in normal operation.

Now, lets look at this a little differently, “Can using one oil versus another for an extended period have an impact on the power output of my engine?” Here the answer is yes, using low-quality oil will result in increased engine wear and increased engine deposits and over time this will result in a loss in engine efficiency and power. Use of high-quality oil will minimize wear and deposits and any resulting efficiency or power losses as the engine ages.


Synthetic oils are too thin for older cars and will cause a high-mileage car to use more oil. Older cars must use conventional motor oils.


Especially for those specifically formulated for higher-mileage engines, today’s synthetics work just fine in older cars. Synthetic is no more prone to leaking than conventional oil. This fallacy might have been created by some synthetics from the early ‘80s.


Synthetics create more sludge.


Synthetics create less sludge: That’s one reason jet-engine makers liked them 60 years ago. Speculation says that this fallacy was created when people switched a vehicle with a poor oil-change history to synthetic. While synthetic may loosen built-up sludge, a change using conventional oil probably will do something similar with a poorly maintained vehicle. When facing such a situation, change the oil filter after about 750 miles and cut it apart to see if it’s filled with sludge.

One more truth: Motor oil is the most important—but the least understood and appreciated—fluid you put in your car.


Motor Oil Specifications:

To many consumers, motor oil seems like the most over-certified product on the market. Some bottles of motor oil bear certification from the American Petroleum Institute (API), the European Automobile Manufacturers’ Association (ACEA), and the International Lubricant Standardization and Approval Committee (ILSAC). A reason for these multiple certifications is the ever-increasing emphasis on reducing vehicle emissions and improving fuel economy, while simultaneously increasing engine power and life. Precise performance from motor oil is required to meet these conflicting goals.

Seals of Approval

Here’s a specific example: Phosphorus in motor oil reduces engine wear, especially in areas of extreme pressure. But phosphorus is bad for catalytic converters, so substances such as molybdenum are partially replacing it. However, rarely is an ingredient an exact substitute for another: It may cost more, be less durable, or create its own issues.

The most well-known motor oil standard was originally developed by the Society of Automotive Engineers (SAE) to measure the oil’s viscosity or how well it flows at cold or hot temperatures. Popularly called the oil’s “weight” or “grade,” the SAE requirements are now part of the other certification processes. If tested both cold and hot, two numbers, such as 5W-30 or 10W-40, describe the grade and the oil is called a multi-grade. Single-grade motor oils are measured at only one temperature and should be limited to engines you don’t care much about, such as your neighbor’s lawnmower.

Test Numbers

The first number of a multi-grade oil comes from cold tests and is followed by a “W”, which stands for winter. The smaller the number preceding the “W”, the lower the test temperatures and the lower the temperature at which the oil will still properly lubricate your engine. The second number comes from tests performed at 100 and 150 degrees Celsius. The higher this number, the higher the temperature at which the oil will still properly lubricate your engine.

Without special viscosity additives, oil won’t perform well at both high and low temperatures: An oil without these special additives that maintains its lubricating properties at 230 degrees becomes thicker than ketchup before you’d need a light jacket. The frequently automaker-recommended 5W-30 is no thicker than a 5W grade oil when it’s well below freezing and no thinner than a 30 grade oil when the engine is up to full temperature. This means the oil will remain both thin enough when it’s really cold and thick enough during normal operation. It’s best to stick with your automaker’s SAE grade recommendations, unless you have extra-special needs—and knowledge.

Viscosity Standards

Understanding the viscosity standards are a breeze when compared to figuring out those from the rest of the API tests, well as those from ACEA and ILSAC. Here’s all most consumers need know: Make sure the oil you buy meets—or exceeds—your vehicle maker’s requirements. For vehicles sold in the U.S., this is most often an API standard. API specs are set as a cooperative effort between the oil industry and vehicle and engine manufacturers from the U.S. and Japan. If your carmaker specifies an API standard, look for the API “donut” or “starburst” on the oil container.

To decode the API donut, first look in the center. There is listed the SAE viscosity. Then notice the top half of the donut where API lists what it calls the “performance level”. It’ll say “API SERVICE” followed by “SL” or “SM”, if the oil is designed for a gasoline engine. (Those designed for diesel engines have a “C” rather than an “S”.) “SL” is recommended only for vehicles from 2004 and before. “SM” was introduced as the top standard in 2004 and API says it’s good for all gasoline-engined vehicles until a new standard appears.

Performance Properties

Each API performance level includes the performance properties of all prior categories. The bottom half of the API donut will either be blank or say “Energy Conserving.” Energy Conserving oils do reduce fuel consumption, however, since our driving habits can have an even bigger effect, typically the benefits of Energy conserving oils can only be seen when looking at a large number of vehicles over many miles.

Some API SM oils may also meet ILSAC’s GF-4. If so, it will say so and there will be the API Starburst logo on the front of the container. Additionally, oils may meet an ACEA standard and if so, it’ll say so on the bottle.

Car and oil companies have been working on a new ILSAC standard—to be called GF-5. This is scheduled to appear in 2011 model-year vehicles, replacing 2004’s GF-4. The car companies have a long list of performance requirements they want improved, some of which required designing new tests. For oil companies, the largest challenge may be making GF-5 workable in 2010 and earlier engines, while meeting the automakers’ new desires. Whether legitimate or not, some vintage-car and hot-rod owners already complain about how GF-4-spec oil performs in their vehicles.

If GF-5 can’t be used in older vehicles, imagine the headaches for auto parts stores, quick-lube places, and do-it-yourselfers. We’re sure the oil-company chemists already can.