Gasoline Grade, Does it Matter?

Every time you pull up to a gasoline pump you encounter those three big yellow buttons with those mysterious numbers labeled regular, mid-grade, or premium.

Which us the right fuel for your vehicle? Is it based on cost? Should it be? I mean if I can afford premium fuel and I love my car then she should get premium fuel right?

Not necessarily.

Those three mystery numbers are the grade of fuel or its octane rating, and what octane you put in your vehicle does matter.

Octane. What does it mean and does it really matter?

noun - Chemistry

"A measure of the ignition quality of gas (gasoline or petrol). Higher this number, the less susceptible is the gas to 'knocking' (explosion caused by its premature burning in the combustion chamber) when burnt in a standard (spark-ignition internal combustion) engine. Octane number denotes the percentage (by volume) of iso-octane (a type of octane) in a combustible mixture (containing iso-octane and normal-heptane) whose 'anti-knocking' characteristics match those of the gas being tested. In the older vehicles, high octane numbers were achieved by adding lead tetraethyl to the gas (the 'leaded gas'), a pollutant that contributes to lead poisoning (see Lead). In the newer vehicles, the same result is achieved by the engine design that increases turbulence in the combustion chamber, and/or by adding aromatic hydrocarbons (such as xylenes) and oxygenates (oxygen-containing compounds such as alcohols) to the gas (the 'unleaded gas'). Also called Octane rating."-

Now you know... right? 

In a nutshell, the higher rating octane means the fuel will resist premature ignition (aka exploding) in the engines combustion chamber. The higher an engine's combustion rating, the higher the level of octane that engine needs to perform efficiently. The higher level of octane combined with the higher combustion results in a more complete burn reducing the fluorocarbons that make their way out of the exhaust system and into the atmosphere. 

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So, how do you know what octane rating is best for your vehicle? The answer is simple. Consult your vehicle's owner manual. It will tell you the recommended minimum octane rating for your particular vehicle and that rating in the US is typically 87 - 89 octane.

That's good for your wallet but not necessarily good for the environment. So wait? Lower octane fuels are not good for the environment? "I love our planet! I'm going to use higher octane fuel to help preserve our atmosphere!" Oh if it were only that simple. If your vehicle's engine isn't specifically built for higher octane fuel, then all you're doing is wasting money. Is will still perform as if it is consuming a lower grade fuel.

What it really comes down to in a stock engine is using the manufacturers recommended minimum fuel rating. Saying that, do not go lower. 

If for example your vehicle's recommended minimum octane rating is 89 (regular) and you find yourself at a station that offers 87, go with the mid grade option. Using a fuel lower than your vehicles recommended rating can affect engine performance and fuel efficiency. 

This is especially important in 21st-century cars where nearly every aspect of engine operation is controlled by computers. Those computers can compensate for a lot, but they are programmed from the factory to operate with a very specific set of parameters and the minimum octane rating is one of these parameters. 

bad gasEssentially, "bad gas" can lead to spark knock due to pre-ignition in the combustion chamber. You may have heard a vehicle that was turned off continue to knock and run or the engine knocks as the vehicle is operating under a load such as going up a steep grade or pulling a trailer. These are often the signs of incompatible octane rating causing premature combustion in the engine's cylinders. 

Run a lower grade fuel for too long, and you will have carbon build up on the inside of the engine. This reduces the efficiency of your engine and can lead to internal damage.

If you're concerned that your vehicle runs on lower grade fuel and you want to keep it internally clean, then your local auto parts store carries a variety of fuel system cleaners and treatments that can help keep your vehicles fuel and combustion systems operating efficiently for 1,000's of miles. Simply using higher octane fuel offers no benefit to your vehicle's engine or to your wallet.

So yes, most cars sold in the US today are rated for 87-89 octane. Performance cars like Camaros, Challengers, and Mustangs often call for a higher grade of octane because of their higher compression engines, but the average vehicle plying our highways is rated for "regular" fuel.