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. 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.
Synthetic oil resists oxidation (thickening), becoming waxy at low temperatures, and volatizing (degrading) at high temperatures.
Although you can expect to pay more for synthetic oil, synthetic oil can let you drive more miles between oil changes. Some synthetic oils suggest 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 by letting you change it less often.
Fuel Economy and Oil
With increased interest in fuel economy, cars have seen a few changes — like the rise of low-rolling-resistance tires and transmissions with more gears. There have also been developments in oil technology that were designed to conserve fuel. 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. It can be hard for consumers to stay vigilant about using the engine-oil viscosity that's recommended for their car. If you choose 10W-30 because there are so many containers of it on the store shelf, you are likely sacrificing fuel economy because you have taken an oil that's heavier than your car needs.
Still, it's tough to find measurable fuel economy benefits just from certain types of oil, and things like wind resistance and tire pressure have a much greater impact on fuel efficiency in the real world.
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.
Oil-life monitors observe things like temperature and engine speed in order to calculate when the oil should be changed. The 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.