The Art of Pumping Gas

Every time we fill up our cars we are usually presented with three choices of gas grades: regular (low octane), mid-grade, and premium (high-octane).

Within these grades, there are three types of octane numbers: anti-knock index (AKI), research octane number (RON), and motor octane number (MON). AKI is the most common octane you will find at the pump. Octane numbers range from 87 (regular gas) to 94 (premium gas).

But how do you know which grade is right for your car? Well, each car is designed to take either low octane fuel or high-octane fuel. Mid-grade is a like filling your car half with regular and half with premium. Most older cars and high performance vehicles require high-octane fuel. There are two reasons why cars require higher-octane fuel. The first reason is a car’s engine is at the upper end of the high-octane range. The second reason is that a car’s octane requirement can increase up to nine octane numbers under the following conditions: frequent short trips, heavy loads, high temperature, and low altitude.

Some newer model cars may have sensors that allow you to go back and forth between regular and premium without any problems. Although your car may be able to run on both types, it makes no difference to engine performance and not worth the price.

The higher the octane number or grade the less likely “knocking” will occur in your engine. Knocking is a sign of abnormal combustion. This occurs when certain components of the gasoline ignite or vaporize before the rest of the fuel inside the engine cylinders does. In the long run, this creates more stress on your engine cylinders and their seals thus resulting in leaks.

But, premium gas does not guarantee improve fuel economy. In fact, getting good fuel economy is not based on gas grades but on good vehicle maintenance and driving style.

Premium gas may also contain oxygenators that allow fuel to burn more cleanly thereby creating less carbon monoxide into the atmosphere. But, these oxygenators can cause the seals in your car to expand. This is only a problem if you switch back to regular. When you do, the seals will contract to a size smaller than it started out creating the possibility of a leak.

The moral of all this is that if you have always used regular in your car, continue to do so. The same goes if you have always filled up with premium. By not constantly switching between regular and premium you will prevent further contraction and expansion of the seals and save your car from problems down the road.