Synthetic & Mineral Based Oil - Black Gold

Oil is literally the lifeblood of an engine. It lubricates by building a film, or cushion, of liquid between moving metal parts. It also acts as a coolant, removing heat from the engine. The choice of a motor oil is determined by bearing clearances, operating temperature of the engine, stresses put on the engine, whether or not you are using an oil cooler, and your preference.

There are two basic types of motor oil—conventional mineral-based oils and synthetic-based oils. There are also different grades or weights of oil. In this article, we will explore the similarities and differences between both types of oil and examine the performance claims made by the oil companies. In the final analysis, only you can decide which oil is right for your car’s engine.

All motor oils are a blend of base stocks and additive packages. A mineral-based oil has petroleum oil as its base stock. The base oil does most of the lubricating of the internal engine components. Unlike conventional motor oil that is derived from petroleum, synthetics are made from manufactured components. They are chemically built molecules. Most companies use esters and polyolefins to build their synthetic structures.

The additive packages vary among companies and are proprietary. The additives enhance and expand the oil’s properties to protect the engine. A buildup of carbon and ash deposits will increase engine wear. For this reason, most oil manufacturers will add detergents to clean these deposits. Adding a dispersant keeps the loosened contaminants in suspension so they can be captured in the oil filter. A byproduct of the combustion process is a buildup of acids that promote corrosion. Rust and corrosion inhibitors are used to coat engine parts to nullify the effects of the acids. Antiwear agents help to reduce friction and promote oil adhesion to engine components. Anti-oxidants reduce the ability of oxygen to react with combustion byproducts that produce varnishes and acids.

Also added to the oil are viscosity index (VI) improvers. They change the weight or viscosity of the oil as the temperature increases. How much and what percentages of each of these additives a company puts in its oil is determined by the need to meet industry standards and what makes economic sense. The additives are the expensive part of the oil formula. According to Joey McClanahan at Valvoline, "The additive packages for the synthetic and conventional oils are different. The synthetic package is far superior. That is why it costs more. Additives are like the cheese on a pizza—they are the most expensive thing."

Weight or Viscosity

The Society of Automotive Engineers (SAE) designates engine-oil specifications. The SAE viscosity grade tells consumers at what temperature the oil is designed to operate. This spec defines the properties of W (winter) oil ranging from 0W up to 25W viscosity. The SAE also specifies standards for straight-grade 20- to 60-weight oils. The W grades are tested at low temperatures. The specification states what the viscosity of the oil must be at a given temperature for engine cranking and starting. For instance, a 0W oil has to have a minimum cranking viscosity of 3,250 cP at minus 30 degrees centigrade (C). A 10W oil has to have a viscosity below 3,500 cP at minus 20 degrees. The requirements for cranking the lower-viscosity oil are more stringent.

In addition to the cranking viscosity, the oil must also meet a pumping-viscosity specification. It does no good to turn the engine over if you can’t pump the oil out of the sump. A 0W oil has to have a pumping viscosity below 60,000 cP at minus 40 degrees C. A 10W oil has to have the same maximum viscosity but at minus 30 degrees C—which is a 10-degree higher temperature. This means a 0W oil must pump at a lower temperature than a 10W oil. The number behind the W is a designation of high-temperature viscosity of the oil. To be classified a certain viscosity, the oil must test within a specific viscosity range at 100 degrees C. A 20-weight oil has to have a viscosity between 5.6 and 9.3 cP, while a 30-weight oil must be between 9.3 and 12.5 cP. Each weight has its corresponding viscosity specification.

High-Shear Test

The high-temperature viscosity grades also must meet a minimum viscosity test at 150 degrees C. It is called the high-shear viscosity test. It measures the viscosity of the oil on a high-speed bearing as a load is applied to it. Each grade or weight of oil must meet a specific viscosity for that grade specification.

The grading of the oil is important because that is how you decide what weight oil to use in your engine. The lower the number, the lower the viscosity. A 5W30 would have better low temperature flow than a 10W30. A 10W40 is not as heavy as a 20W50. It would have a better cold-pour characteristic but would also have less high-temperature protection. The SAE viscosity classifications are the same for synthetic or mineral-based oils. Some companies are making claims that their synthetic oil has a viscosity index below 0. The lowest SAE grade is a 0W. There are no double- or triple-zero oil specifications. A company can call its oil whatever it chooses. Anything below a single 0 is meaningless.

Another body that regulates oil is the American Petroleum Institute (API). It sets minimum specifications for oils and oil additives for street engines. The API donut on the container will show which standard that oil meets. The S is for gasoline, and today’s top specification is SJ. Without the API approval, it’s difficult to tell if an oil meets any specification. If the oil is strictly a race oil or marine oil, it may not have the API donut.

Multigrade

Most oils used today are multi- grade oils. A multigrade oil changes viscosity as the temperature increases. Obviously, these oils have many advantages. The first number before the W represents the cold-temperature-flow characteristics of the oil. The lower the number, the better it will flow when starting a cold engine. A lower number after the W means the oil has less parasitic drag. It takes less energy to pump the oil when the engine is hot, therefore more power is available at the rear wheels. Lower viscosity oils do not make power; they just rob less of it.

The other advantage to multi-grade oils is you can match the second number to meet your engine’s high-temperature needs. For instance, a 10W30 or 10W40 would have the same low temperature flow, but the 10W40 weight would have more viscosity protection at higher temperatures.

The disadvantage of multigrade oils is they use viscosity index (VI) improvers to change the viscosity of the oil. Viscosity improvers are specially formulated polymers made of long chains of carbon and hydrogen atoms. At extremely low temperatures, they curl up in a little ball.

As the temperature increases, the balls of atoms expand, straighten out, and become longer. As they become longer, they contribute to the viscosity of the oil. At high temperatures, these long polymer chains spread out through the oil and have a tendency to thicken the oil. There is a physical change to a multigrade oil as it heats up.

As with most things in life, too much of a good thing is bad. Adding too many polymers to a thin-base oil is not good. The wider the range between viscosities, the more polymers that must be added. A 0W50 oil will have more viscosity index improvers than a 20W50 oil. The problem is the polymers break down or are sheared and can no longer increase the viscosity of the oil. They break up as the oil flows through the engine and squeezes through 0.002-inch bearing clearances. They pull apart when sucked through the oil pump. The oil can start as a 20W50, but over time it could become a 20W30 because the polymers are physically broken down and can no longer thicken the oil.

Synthetic Oil

The other type of motor oil that is touting superior protection and lower frictional drag is synthetic oil. Unlike conventional, petroleum-based oil, synthetic oil is manufactured from chemically built molecules.

There are numerous benefits to synthetic oil. It has much better low-temperature flow properties. It will flow at much lower temperatures than conventional mineral-based oil. Synthetics generally have lower volatility. Volatility is how quickly the oil vaporizes inside the engine as it is operating. This means synthetics have better high-temperature protection. The synthetic oil does not boil as readily at higher temperatures as a mineral-based oil would.

Bob Pache of Mobil Oil, which makes Mobil 1, describes some other benefits of synthetic oils. He says, "Because of the synthetic nature and cost of the base oil, we have the opportunities to use the better-performing—or more costly—components, when blending the motor oil. "As far as performance advantages go, there is extended stability. It can take a tremendous amount of heat. In racing applications, where a car can go up to 400 degrees, the engine will survive.

"Synthetics seem to have better antiwear characteristics in that they have better film strength. Multigrade conventional oils have to use viscosity index (VI) improvers to thicken the oil. Synthetics generally use some improvers but not as much, because they have a naturally high VI. They resist the tendency to thin out at high temperatures as fast as conventional oils.

"They have improved fuel economy benefits. It improves fuel economy by reducing friction. That correlates to increased horsepower."

Higher Cost

The main drawback to synthetic oil is the cost. Because the base oil is more expensive, the manufacturers have decided to not compete with mineral-based oils on cost. Instead, they formulate the oil using expensive additives. Their marketing philosophy is "the best costs more." Valvoline makes conventional, synthetic, and a blend motor oil. The company’s Joey McClanahan explains the difference, saying, "Synthetic oil is like getting a fancy paint job or fancy rims. It adds to the overall car. It’s not necessary, but it does provide you with a lot of extra protection. If you change your oil regularly with conventional oils, you will never have any problem. But if you change your oil and use synthetic oil, you are going to be getting a lot better lubrication protection, cold start protection, less wear, more horsepower, better gas mileage, and a cooler-running engine because it is a more efficient running engine.

"If you want the best money can buy, a synthetic is the best way to go. If you just want to get by with protecting your engine as much as it needs and saving as much money as you can, use a conventional oil. If you want the best of both worlds, then you want a blend because it provides a lot of the same protection a synthetic does at half the price."

To offset the higher cost of synthetic oil, some of the oil companies claim you can run the oil longer between changes. They say you do not have to change the oil every 3,000 miles. Valvoline does not make that claim. McClanahan says, "The additives in synthetics are superior but they still break down at the same rate and you need to replenish them often. We are unaware of any additive package that lasts longer than what the manufacturer recommends. Those 10,000-mile claims are ludicrous."

The base oil is good forever. The additives and VI improvers break down over time. The thing that destroys the ability of the oil to lubricate is the accumulation of gasoline, dirt, and engine contaminates in the oil. Oil is supposed to get dirty. Its job is to remove contaminants out of the engine. Even with the superior additive package of the synthetic, contaminates still accumulate and need to be flushed out of the engine. Therefore, you need to change your oil often.

Every time you change the oil, you must change the oil filter. The oil filter traps the dirt. By adding new clean oil and not changing the filter, all you are doing is adding dirt to the clean oil. An oil filter has a relief valve that allows oil to pass through the filter when it is full. A that point, you are circulating dirty oil.