Choosing the Correct Octane Fuel For Your Vehicle

August 25th, 2014 by

Putting the Right Octane Fuel In Your Vehicle

Ever wonder why there are so many gasoline choices at the pump? You almost always have the choice of regular, mid-grade, or premium; sometimes you are presented with even more options. Each of these options is associated with a different octane rating, do you know what it all means?

What Fuel Octane Ratings Mean

To explain the octane rating, let’s take a minute to refresh ourselves on how an engine works. Inside each cylinder, a piston compresses a gasoline and air mixture, which is ignited by a spark plug, which results in an explosion that pushes the piston back down and ultimately drives the vehicle. Since there are multiple cylinders in a car, the explosions must be times very precisely. The octane rating of gasoline describes how much fuel can be compressed before the fuel spontaneously ignites. That is to say, the fuel becomes so compressed that it explodes, versus being ignited by the park plug. The higher the octane, the higher compression the fuel can handle before igniting.

How Most Engines Burn All Octane Fuel

Simply Shown How Most Engines Work

Putting the Wrong Octane in your Engine

Damaged Engine Parts

The Type of Damage Cause From Improper Fuel


Putting a fuel with an octane rating that differs from what the manufacturer recommends can have varying effects. If a car is designed to be run with high octane fuel, running a low octane fuel may throw off the vehicles timing. As the gasoline and air mix in each cylinder becomes compressed during normal operation, an explosion may occur before the spark plug ignites. Since the timing of the explosion is incorrect the vehicle may develop a “knock”, or the incorrect timing may put serious stress on engine components and ruin the motor. In vehicles designed to run on a low octane fuel, adding a higher octane will usually cause very few changes. It is possible that a higher octane fuel will not burn completely before exiting the cylinder in the form of exhaust; in this case a higher octane fuel may foul your vehicle’s catalytic converter or cause a decrease in gas mileage. In most cases, running a higher octane fuel than what is recommended for your vehicle is just a waste of money.

Why Running a Lower Octane at High Altitude is Recommendedhigh altitude road

You may have noticed on your last vacation to the beach that it’s a bit hard to breathe in Colorado. It’s easy to forget that we are at a pretty high altitude here in Boulder. It is for this reason that in most parts of Colorado “regular” gas is rated 85 octane instead of the 87 octane found in other states. Since the air that your car breathes is thinner in Colorado, compression in each cylinder is lower that it would be at sea level. There is some controversy over the matter, but a lower octane gas is in most cases just fine. At altitude it is typically OK to run a fuel with an octane that is 2 points lower than what is recommended by a vehicle’s manufacturer, so if your vehicle is engineered to run on 87 octane, 85 will do. At sea level, it is never a good idea to run a fuel with a lower octane than recommended.  Check your vehicle’s manual to see what type of fuel it is designed to run on and act accordingly.

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