Does the Gasoline Type You Use Matter That Much?


In the past, fueling up your vehicle was pretty simple. You picked unleaded or diesel, and that was about it. Now, however, there are seemingly endless choices when you go to the pump. Along with such, there are name-brand stations and discount stations, making it tough for people to decide which one is right for them.

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In the past, gasoline was dispensed from pumps that had glass globes atop them, allowing motorists to see the quality. Gas quality now is heavily regulated and, by law, must contain a variety of ingredients, such as octane, detergents, and ethanol, among others. Name-brand gasoline might have more detergents than others; many times, off-brand gasoline is likely produced by the same manufacturers you know and trust. Therefore, you can purchase gasoline wherever it’s convenient and wherever it is less expensive.

Should You Pay More for Higher Grades?

You can usually find three different grades of gasoline (unleaded) at US gas stations. The price you pay (per gallon) is likely to rise with the fuel grade. The grades are really octane ratings, and they matter depending on the type of vehicle you drive. High-performance engines require higher octane fuel because the engine is designed to generate a higher compression within your cylinders to increase power. It’s not conducive to have lower octane and higher pressure. Along with such, high-performance engines can have decreased performance and power if they don’t get the higher-octane fuel.

If you’re unsure of the octane level you should be using, you can look in the owner’s manual. You can also experiment with different octane levels to see which one gives you the best performance. If the vehicle runs well without pinging, knocking, and other problems, it doesn’t hurt to choose a lower grade of fuel.

Knocking Engine

Many people wonder if the octane level causes a knocking engine, but you must first understand why it knocks and why it’s important that it doesn’t. When the octane rating skyrockets, the gasoline’s ability to compress without igniting also goes up. The air/fuel mixture inside your cylinders should only ignite the gasoline when the spark plug creates a small flame. The flame grows gradually and spreads, allowing the fuel/gas mixture to ignite in a single detonation. When an audible knock is heard, it means multiple detonations have occurred within your cylinder.

While annoying, it also destroys the engine over time and robs it of power. The higher-octane fuels can withstand the increased compression, which prevents the spontaneous detonations. However, gasoline isn’t the only issue that can cause knocking. Other issues can include faulty spark plugs, more load, a cooling system that malfunctions, your environment, and the vehicle’s age, among others.

Is It All Unleaded?

Some drivers might remember when they could choose between unleaded and leaded fuels. However, GM and ESSO (Exxon) realized that if they added tetraethyl lead to the fuel, the octane ratings were raised above what was listed. Leaded fuel also helped protect the valve seats. When the engine was in operation, the heat from the combustion gases caused the valves to weld themselves to the valve seats temporarily. Each time that happened and the weld was broken, tiny metal pieces were torn away and attached to the valves. These deposits hardened, which damaged the valve seat. The lead helped the two items from welding together. However, lead is also highly toxic, so it was phased out in the 1970s.

Since you can’t get leaded fuel anymore, you may want to install a hardened valve seat or replace your cast-iron heads with alloy versions; you can also find lead substitutes for the gas tank.

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Does the Gasoline Type You Use Matter That Much?

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