Like the cars it's used in, engine oil has steadily evolved over time. Today's motor oils can be used for much longer mileage intervals, thanks in part to the development of synthetic oil. And the consumer benefits don't stop there.
What is Synthetic Oil?
The term "synthetic oil" can refer to either man-made base stocks or highly refined petroleum base stocks, according to Dennis Bachelder, a senior engineer at the American Petroleum Institute. Synthetic motor oils go by various names, like Mobil 1, Castrol's Syntec and Valvoline's SynPower, and they have some general advantages over conventional oils.
Ray McDonald, Global Technical Adviser for Mobil 1, says synthetic oil resists oxidation (thickening), becoming waxy at low temperatures, and volatizing (depleting) at high temperatures.
You can generally expect to pay more for synthetic oil, according to McDonald. An online search at industrial supply company Grainger revealed that a quart of ExxonMobil's Clean 5000 10W-30 motor oil would cost $5.25, but a quart of synthetic 10W-30 Mobil 1 would be $12.30.
Synthetic oil can also let you drive more miles between oil changes. AMSOIL's Signature Series 0W-30 synthetic oil has a service interval of 35,000 miles, or one year for non-severe driving. This longer interval can help offset the higher cost of synthetic oil.
Fuel Economy and Oil
With increased interest in fuel economy these days, cars have seen a few changes, like available low-rolling-resistance tires and transmissions with more gears. There have also been developments in oil technology designed to conserve fuel.
"Fuel economy is a major driver, and that's why you're seeing a lot of the thinner oils," said Ed Newman, director of advertising for AMSOIL.
"The other big driver of engine-oil technology is robustness," McDonald said. He noted that engine advancements are resulting in smaller engines that work harder, which puts greater stress on the oil inside them.
In some instances, though, it's less about the oil and more about the person changing it. Dewey Szemenyei, chair of SAE International's engine lubrication committee, said it can be hard to convince people to use the engine-oil viscosity that's recommended for their car. "When you take a look at the oil on the shelf, there's more 10W-30 on the shelf than any other viscosity grade," he said. If that's heavier than their engine needs, "they're sacrificing fuel economy in the process."
That said, Bachelder said it's tough to measure fuel economy benefits associated with a certain type of oil, and that things like wind resistance and tire pressure have a much greater impact on fuel efficiency.
You used to have to keep track of when to change your oil, but some newer cars with oil-life monitors will do it for you, letting you know when it's time to seek service.
"The manufacturer believes enough in those that they're putting the warranty behind them," Bachelder said. "It's a better gauge of what the oil has been exposed to than the three-month or 3,000-mile intervals."
McDonald says oil-life monitors observe things like temperature and engine speed in order to calculate when the oil should be changed. He also adds that its calculations are based on the oil recommended for the engine. That means high-performance synthetic oil won't necessarily result in a longer service interval from the oil-life monitor even though the oil may be able to handle one.
Perhaps the monitor's most important benefit, however, is a simpler one.
"It helps remind people that their oil needs to be changed," Szemenyei said.