Mark McFann of Royal Purple
It's hard enough to understand things that you can see. For instance, electronic fuel injection, Rubik's Cubes, and those with the double-X chromosomes. As utterly baffling as they may be, things get a bit more perplexing when you can't even see the subject you're trying to comprehend. Such is the case with motor oil. It all looks the same, whether it's pouring into your valve cover or leaking out of your rear main seal. However, each brand claims to be the best, so the stuff must be different, right? While we won't attempt a definitive judgement on who mixes up the best lube, we did sit down with Royal Purple Vice President of Marketing Mark McFann to get the scoop on the chemistry behind motor oils. Although modern oils are incredibly complex, Royal Purple explained things in a way that doesn't require a chemical engineering degree to understand.
When synthetics first stated appearing in the mid-'70s, there was some truth to the old wives' tale that they can cause leaks. Back then, synthetics were used primarily in race motors but in very few street cars. "Some of the original synthetics were formulated with high concentrations of diesters, which created seal compatibility issues," explains Mark. New-car manufacturers at the time weren't ready for synthetics. However, the OEs and oil manufacturers have worked together to solve these problems, and many new cars now come with synthetic oil from the factory. Although it's very rare, there have been instances where high-mileage motors that switched to synthetic oils did experience leaks. Modern formulations have small amounts of ester, but they can promote solubility and clean up deposits that were left behind by mineral oil. "If those deposits had become part of the tolerances around a gasket or seal, then synthetics can clean that out and expose those areas," Mark says. "In a situation like that, the oil itself isn't so much causing the leak as it is exposing an existing problem."
How Lubrication Works
Lubrication can be broken down into three states. Hydrodynamic lubrication describes the ideal situation, where a continuous film of fluid separates two sliding surfaces. The viscosity of the oil supports the entire load between moving parts and prevents them from touching. On the other hand, boundary lubrication is the last line of defense before metal-to-metal contact occurs. When oil is squeezed out from between moving parts in high-load areas (i.e,. between main journals and bearings), all that's left to prevent excessive wear are antiwear additives. Mixed-film lubrication is a little bit of both, where some oil has been squeezed out but a marginal coat of oil is still present. Oil is present in each state somewhere in the engine, which is what makes formulating oils so complex. "Unfortunately, you can't have hydrodynamic lubrication under all conditions, which makes the additive package of an oil that much more important," explains Mark.
"A popular misconception is that synthetic oil is magically created in a beaker," says Mark. "The truth is, all oil comes in a natural state, and all oil starts as crude. The difference between a synthetic and a mineral-based oil is just a matter of how that crude is processed. Synthetic oil is highly refined crude with molecules that have been realigned by man. This makes them significantly different from what they were in the ground. As a result, synthetics have a uniform molecular size and lower traction properties, reducing friction. Crude has lots of impurities, but they are removed during refining when formulating a synthetic oil. However, that's not to say synthetic oils are always better than mineral-based oils. These days, additives are even more important than whether base oils are mineral or synthetic."
"Viscosity simply refers to the thickness of an oil, and oil weights are just a means of expressing that thickness," Mark says. "The Society of Automotive Engines (SAE) sets criteria for different viscosities that oil manufacturers must adhere to when rating their oils at a certain weight. There are two numbers in the SAE rating system. The first number-the 10 in a 10W-30 oil-indicates the cold-weather thickness of the oil. A lower number means thinner oil, and therefore better cold-weather properties. If you're in Alaska, a 0W would be the way to go, and if you're in Texas, a 10W would be sufficient. The second number-the 30 in 10W-30-reflects its viscosity at operating temperature. In high-heat environments, a thicker oil may be preferable. The way we test viscosity in a lab is by measuring how fast a drop of oil sinks to the bottom of a fluid-filled test tube at a given temperature. Think of it as a funnel with a restricted orifice. The heavier the viscosity, the slower it flows through the tube. Straight weights only measure the thickness of oil at operating temperature, but are very uncommon these days, due to advances in additive technology. There are no downsides to using multiweight oils, and they improve fuel mileage as well."
"Heat is a catalyst for a chemical reaction between oxygen and oil, also known as oxidation," Mark explains. "When oxidation occurs, it attacks the chemical composition of the oil and changes its molecular structure, which forms acids and creates sludge. Due to the lower level of impurities in the cross-linked molecules of synthetic base oils, they are more impervious to the effects of oxidation. Combined with quality chemical antioxidant additives, synthetic oil can last for extended periods of time. If a mineral oil and a synthetic oil were formulated with the same additive package, the synthetic would last longer because it's not going to deplete its antioxidants as quickly."
From a lubrication standpoint, race oil is far superior to street oil. This is because street oil is bound by API restrictions, which limit the amount of antiwear additives that can be used in street cars, since it's believed that they can deteriorate catalytic converters when used in high concentrations. "All the good stuff you'd normally put in a racing oil you can't put into street cars because of limitations set by the API," explains Mark. "The government is more concerned with emissions than ultimate lubrication properties." That being the case, can racing oil be used in street cars? The PC answer: only if your manufacturer's warranty has expired; most racing oils have the detergents and dispersants necessary for daily use. In order to facilitate maximum performance, racing oils vary in viscosity compared to street oils, so be sure to consult with the oil manufacturer before making the switch.
It's odd to think of a fluid as something that can shear, but that's exactly what happens to oil over time. In areas where oil is squeezed-such as in an oil pump, between rings and cylinder wall, and around crank journals-oil molecules permanently shear over time, resulting in a loss of viscosity. To compensate for viscosity loss as oil breaks down and heats up, viscosity index improvers are added to the formulation. "To put it simply, VI improvers have polymers that wad up under heat and behave more viscously," says Mark. "In the early days, the polymer chains in VI improvers would shear so much that a 5W-30 would turn into a 5W-20. However, with today's advances in modern polymer quality, that's no longer an issue. A big advantage of synthetic base oils is that they experience very little permanent viscosity loss and don't rely as much on VI improvers."
Think of the American Petroleum Institute (API) as the watchdog of the motor-oil industry. In conjunction with auto manufacturers, the API has developed a set of quality standards for various classes of oil. "Whereas the SAE tells you nothing about oil quality-just viscosity-the API actually tests the lubrication properties of an oil," explains Mark. New-car makers use the API to establish a benchmark for oil quality for warranty purposes on engines. "The API will routinely go around the country pulling random samples off the shelf to verify oil quality coincides with what a manufacturer claims, and also to make sure a package is labeled according to their standards," Mark says. "If something is wrong with an oil sample, the oil manufacturer is immediately notified to correct it."
The API's quality standards are broken down into several classes, or grades, that rate oils based on their wear and oxidation properties. A two-letter designation-such as SJ, SL, and SM-is given to each oil formulation as an indicator of its lubrication properties. Every few years, the API establishes a new benchmark that supersedes all previous grades of oil. In theory, an SM-grade oil offers superior protection to that of an SL, and an SL formulation should outperform an SJ. However, this isn't always the case. "As API standards continue to evolve, these days it's more concerned with increasing oil life and reducing the potential for oil to contribute to emissions," says Mark. This has led many industry insiders to come out and say the newest SM grade oil falls short of the wear protection offered by the SL grade it replaced.
"Lubricating oils are fairly complicated in terms of all the different ways they can be formulated, and quality depends on how much money someone wants to spend creating a formula," Mark says. "Roughly 80 percent of a motor oil is composed of the base oil, and the other 20 percent is made up of additives. The role of antioxidants is pretty self-explanatory. Corrosion inhibitors neutralize acids to protect against rust. Antiwear agents adhere to metal surfaces to prevent wear in areas prone to metal-to-metal contact. Extreme pressure agents take over under high pressure and heat when normal antiwear agents would fail. Dispersants fight sludge buildup by keeping small contaminant particles in suspension. Depressants improve flow at low temperatures. Demulsifiers promote the separation of water from oil, and antifoam agents release air trapped in the oil."
When subjected to extreme heat for a long time, such as on a road course, synthetics offer significantly improved protection over conventional oils. "For every 18 degrees F that oil temperature increases, the rate of oxidation doubles," explains Mark. "If oil temperature increases from 200 to 218 degrees, oil life is cut in half. In other words, those last few degrees of temperature increase are severe." Extreme heat breaks down low-quality oil much more quickly than a high-quality synthetic. Highly saturated with molecules and free of impurities, synthetics are much more stable at high oil temperatures and reduce friction. Lower volatility also cuts down on the evaporative losses.
While synthetic oil provides excellent wear and high-temperature protection, it's not invincible. With aftermarket high-flow air filters come the potential for increased dust transmission through the filtering media, especially if they're not regularly cleaned. "Unlike the adverse effects of heat, water, and oxidation that can be counteracted with additives, oil can't overcome abrasives," says Mark. "Any abrasive particles not trapped by a filter can score the engine. The same goes for metal particles, which is why filter magnets, while not mandatory, are a cheap and effective line of defense." The only way to remove abrasives is by changing the oil, which should be done more frequently in dusty environments and with freshly rebuilt motors.
Engines breathe even if they're just parked, as moisture in the ambient air condenses and expands inside the oil pan. Short trips are hard on oil because they don't allow it to reach operating temperature for sustained durations of time. "If you never get oil up to temperature, you'll never get the moisture out of the oil," Mark says. Water is a catalyst for oxidation, so the higher the water content, the greater the oxidation. "With industrial equipment, there are drains that remove the water that sinks to the bottom of the oil," he adds. "Since an engine is not designed that way, the only defense against condensation is to get the oil up to temperature. There isn't a set target temperature, but the higher and longer you run the motor the faster water burns off."