MUNDANE MYSTERIES: What Are The Numbers On Gas Pumps?

Whenever you gas up your car, you’ll always see a certain set of numbers on each pump…usually 87, 89, and 93. What are those numbers? And what do they mean?

Those numbers on the yellow buttons on the gas pumps actually denote each fuel’s “octane rating”. The Regular 87 octane rating gasoline is what most folks typically buy. The Mid-grade’s gas rating is usually either 89 or 90. And then, for Premium gasoline, the rating will usually land somewhere between 91 & 94.

Basically, octane ratings measure each fuel’s stability. To make your car run, the engine’s spark plug lights a flame that generates what’s called a “controlled combustion”, whereby it gradually burns all the fuel in the cylinder. Under certain conditions, however, rising temperatures & the combustion’s pressure can lead unburned fuel to ignite without the spark plug flame. That “uncontrolled combustion” raises the pressure in the cylinder & could potentially damage your engine. Uncontrolled combustion, or “knocking”, isn’t really a problem nowadays, though, since almost all commercial fuel now is made with an oxygenate that keeps it from prematurely igniting.

Octane ratings specify how high the fuel’s oxygen content is, with the lowest digits being the ones most likely to experience uncontrolled combustion. To measure a fuel’s R.O.N., or “research octane number, the gas gets tested in an idling vehicle with low air temperature & slow engine speed. Then, to measure the M.O.N., or “motor octane number”, the gas gets tested under high temperature & high engine speed. Then, those two numbers get averaged together & that gives you the octane rating.

The combined effects of oxygenated fuels, computerized ignition, and knock-detecting sensors have all pretty much helped to rid today’s vehicles problems with uncontrolled combustion. So, for most folks, the Regular 87-octane gas is perfectly fine. However, certain cars genuinely do need premium gas, meaning high-grade fuel is the most efficient choice if you have a high-performance vehicle. In any case, whether your car is luxuriously lavish or a middle-of-the-road model, it’s usually going to be worth it to pay a little extra for the gas that’s least likely to mess up your motor.

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