Additives
"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."
Extreme Heat
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.
Abrasives
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.
Short Trips
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."
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