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.
Leaks
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.
Synthetic Basics
"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."
Oil Weights
"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."