Premium vs Regular Gasoline

Premium gasoline must be premium for a reason. After all, one of that adjective’s definitions is “a high value or a value in excess of that normally or usually expected,” according to Merriam-Webster’s Collegiate Dictionary. Therefore, premium gasoline must be better, otherwise why would it be called premium? The answer to that question lies in the dynamics of the typical internal combustion engine, the process of refining gasoline from oil, and another definition of “premium”—this one from its noun form: “a sum over and above a regular price paid chiefly as an inducement or incentive.” For standard cars on the road today, purchasing premium gasoline is simply paying a premium for a fuel that delivers no added benefits.

First of all, premium gas is more expensive, typically 20 cents a gallon more expensive than regular, because it contains a higher percentage of octane. Why is this important? When vaporized gas mixes with air and fills the combustion chamber, it is compressed by the rising pistons. This makes the gas-air mixture grow hot and it could ignite before the spark plug fires, pushing backward on the piston. Higher-octane fuels can be compressed to a greater degree without self-igniting. In the old days, engines could not adjust to fuels with varying octane ratings. Use the wrong fuel and the engine would knock or “ping” audibly because the gas exploded prematurely. This knocking damaged internal engine components over time. Today, engine control systems can compensate for low octane by monitoring knock activity and adjusting ignition advance to avoid knocking.

The key for drivers is to know whether premium gasoline is merely recommended or if it’s required. In today’s automobiles, advances in engine technology mean that even if the owner’s manual recommends premium gasoline, the car will typically run on regular without issue and won’t damage the engine in any other way. The car’s performance might suffer only slightly: it might be a half-second slower from zero to 60 mph, for instance. But the average driver isn’t likely to notice this drop-off.

It’s a different story for a car whose engine requires premium fuel. The car will still run on regular fuel in a pinch, but you shouldn’t make a habit out of it. The fuel’s lower octane can adversely affect the engine’s health in the long run. Running regular-grade fuel in a car that requires premium might sound like a good way to shave a car’s running costs, but the short-term savings won’t come close to offsetting the cost of repairs to a damaged engine.

Edmunds has compiled two lists: “premium recommended” and “premium required” for vehicles from the 2009-2014 model years (with a few 2015 model-year vehicles). If your vehicle is on the “premium recommended” list, you’re OK to try switching to regular unleaded gasoline. If, on the other hand, your car is on the “premium required” list, then you have to run premium fuel. You can confirm the information on these lists by checking your owner’s manual.

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