Over time, tiny contaminants invade the oil, like combustion byproducts, miniscule metal fragments from the engine, and a sludge created by the continuous cycle of heating up and cooling down.

For example, some engine oil features a prominent C on the packaging, but what does this mean for what it can be used in?

"In the 1970s we got our first taste of what it was like ... oil and ethanol? Actually, the combination of those would seem to fit nicely into today's engine structures," he says. Fuels aren't the ...