Watch: What does fuel octane rating mean, and what happens if you put the wrong fuel in your car?
16-minute explainer clears up misconceptions — and shows the consequences of incorrect octane and dirty engine components
We’ve been burning gasoline for well over a hundred years now, but some misconceptions about fuel — especially when it comes to octane — are so ingrained in the popular consciousness that even those of us who know better slip up.
Consider: We commonly use “high octane” to describe something with more power, or more broadly an experience that’s super intense. This is a bit like saying that you’ve “kicked something into overdrive” when you mean to say you’re going faster or harder, or calling a high-performance electric car a “Turbo.” As the above video by YouTube’s ChrisFix explains, when it comes to the octane rating of gasoline, that’s not the case: A given quantity of 87-octane gas has the same stored energy as the same amount of high-test fuel.
Rather, the octane rating is a measure of a fuel’s resistance to detonation, wherein a fuel/air charge explodes unevenly within an engine cylinder rather than combusting smoothly. These detonations, also known as engine knock, reduce efficiency and output in the best case and can destroy an engine in the worst case.
So it’s important to use the correct octane fuel in your car. Generally, this isn’t complicated: For an unmodified car, use whatever the manufacturer recommends. If it’s not indicated on or near the fuel filler cap, it’s in the owner’s manual.
In general, modern cars are less picky about what they drink thanks to technology: A knock sensor, for example, attempts to detect detonation caused by a less-than-ideal octane and adjust engine timing to correct it. This is why some newer cars merely recommend premium fuel, rather than requiring it; using gasoline with a lower octane rating may reduce efficiency and performance, but it won’t cause your engine to knock itself onto the scrap heap.
It gets a little trickier with old vehicles or modified late-model cars. In the case of the former (at least in the world of early 1950s stock flathead your author deals with), the consensus seems to be that 87 octane is fine — the great ethanol debate aside, even low-grade gasoline today is more predictably high quality than what was available at America’s service stations decades ago.
In any case, it’s better to use fuel with too high of an octane rating than too low: Worst case, you’re burning money for no performance or efficiency gain.
The video, which also delves into the world of fuel additives, is designed for as broad an audience as possible (as an Autoweek reader you no doubt know not to, er, put diesel in a gasoline car, and vice versa). But even if you understand the fundamentals, it’s great to see how everything works — or doesn’t work — in action, something this video accomplishes via computer animation and real-life test rigs.
Thanks to Jalopnik for putting this useful video on our radar.