From octane levels to ethanol percentages, leaded vs unleaded and everything in between, gasoline is a lot more complicated than “regular” or “premium" grades.
Whether you’re interested in fuel economy, high performance, or just want to know what types of gasoline you can put in your car, this is everything you need to know about the different types of fuel available at gas stations.
Your car’s engine does one very important job: It converts fuel into movement. To do this, small amounts of fuel are pumped into cylinders where they are ignited by a spark plug. Compression is what makes that tiny explosion powerful enough to move the pistons.
How much compression each car engine needs can vary based on the construction of the engine. You can find out what your car’s engine is considered by using the owner’s manual, which should also tell you what the desired octane rating is for your vehicle.
The largest printed number on a fuel pump refers to the octane rating. Every car has an “optimum” octane number that’s based on the engine’s compression needs.
Despite how gas stations label their pumps, the actual classifications of octane ratings are not ‘good, better, best’ and putting premium gasoline into a car with an 87 octane rating isn’t going to turn your car into a track beast.
Octane rating doesn’t measure the quality or the power of gasoline; it measures its volatility. Higher octane numbers are the least volatile and are used in performance gas-engines that require higher compression ratios. If you have a car with a performance engine and you fill it with lower octane fuel, you may notice engine knocking. That’s because there’s just more explosion occurring than that car needs to move its pistons.
In short, more explosion doesn’t move the car faster, it just makes a little more noise.
On the other hand, if you fill a car with an optimum octane rating of 87 with gasoline rated at 93, you won’t go faster or farther. Lower volatility also means lower energy, so if anything you would notice the car feeling a little laggier than it might otherwise. The good news is that using a higher octane fuel in an engine that has a lower rating won’t hurt the engine.
Unleaded vs Leaded
If you’ve ever stared at the label on the "regular" gasoline that simply says "unleaded" you’ve probably had some questions. Like is this my only option for gas that doesn’t have lead in it? Why would there have ever been lead in gasoline to begin with?
None of the gas you can purchase at a gas station today will have lead in it, though leaded fuel is still used in some places for a variety of applications.
During the 1920s, lead was used as a gasoline additive to reduce engine knock. Knocking was caused by gas pre-igniting. Lead is what’s known as an “octane booster,” an ingredient you can add to gasoline to increase its octane rating.
Though the plus sides sound great, lead has a reputation as a toxic substance for a good reason. Having a nation full of vehicles burning lead daily had major repercussions for the overall health of the population, and soon there were noticeable national symptoms.
Between 1976 and 1980 use of leaded gasoline dropped by 50% in the United States, and the average level of lead found in the bloodstream of the populace dropped by 37%. Since then we’ve discovered a host of other less problematic detergents to use to prevent engine knock. However, leaded gasoline is still used in race cars because of its ability to act as an octane booster.
The other problem with leaded fuel is that it doesn’t play well with oxygen sensors or catalytic converters. The lead coats the catalytic converter, rendering it useless. These parts need to be removed from race cars hoping to utilize leaded gasoline.
Another option for people who want a fuel additive that will increase the octane rating of their gasoline is ethanol. Ethanol is being used as a fuel additive and octane booster, but not just in race cars. It’s likely that either currently or soon you’ll see more gas stations advertising the ethanol ratio of their gasoline.
E10, E15, and E85 all refer to ethanol blends. The number (10,15,85) refers to the percentage of the fuel that’s comprised of ethanol.
Ethanol is a biofuel, which means it’s made out of biological matter and is a renewable fuel. A lot of different “biological matters” can be used for this, like sugar cane or sweet potato.
Ethanol can also be made out of corn, though this process is less efficient than with other biological matter. The Environmental Protection Agency (EPA) is in favor of ethanol blends because they reduce greenhouse gases and are better for the environment than fossil fuels, and many performance drivers use E85 because of its high octane rating. What it means for you and your car depends on the percentage of ethanol to gasoline.
E10 fuel is an ethanol-gasoline blend consisting of no more than 10% ethanol. Most modern vehicles don’t need any modifications to run E10. Though ethanol has less fuel economy than gasoline, at 10% ethanol the effect is only around -3% fuel economy. Many gas stations are already selling E10.
E15 is a gasoline blend consisting of no more than 15% ethanol. Unlike E10 however, it is not recommended for all vehicles. Soon there will be more gas stations selling E15 blends, and it’s believed that it will help keep fuel prices more reasonable. Though cars with model years 2001 and newer should be compatible, it is still worthwhile to check out your individual car’s specifications for compatibility. Some car manufacturers have gone as far as to say that use of E15 voids vehicles’ warranty and they won’t be responsible for damage to fuel lines, fuel systems, or engine components of vehicles that are using ethanol.
E85 is 85% ethanol and is sometimes referred to as FlexFuel. Before filling up with E85 you will need to check to see if you’re running a FlexFuel vehicle. (Almost 68% of FlexFuel vehicle owners had no idea what that meant or that they could use E85). If you don’t, you’ll need an adapter for your engine to be compatible with E85.
E85 is considered a high-performance fuel. Its octane rating is higher than premium unleaded. Because of its incredibly low volatility, it can be run with more boost and compression and still be immune to detonation.
E85 is where the loss of fuel economy in ethanol blends becomes noticeable. You’ll notice about 25% lower fuel efficiency when compared to normal unleaded gas. Though FlexFuel vehicles can use E85 now, most other cars, especially older cars, require a conversion in order to use it that may or may not be worth it to you depending on how many gas stations in your area even offer E85 as an option. Right now E85 is only offered at a little over 3,000 gas stations in 42 states, which means it’s not a viable option for everyone.
Premium vs Regular Gasoline Infographic
[click the infographic below]
Sources: EPA | BBC | Smithsonian | U.S Department of Energy