Do you know what kind of fuel to put into your car?

Confusion at the Pumps: How to Choose the Right Fuel 

Have you ever pulled up to the gas station to put gas in your gar and wondered: what type of fuel should I put in my car? If you’re confused at the gas pump, you’re not alone.

In the United States, there are primarily two types of common automotive fuel: diesel and gasoline. According to overall sales in 2014, gasoline is the most common fuel used. Gasoline powers more than 98% of all light duty vehicles in the States, with diesel following in a distant second at 1.5%*.  Light duty vehicles include all passenger cars, pickup trucks and sport utility vehicles.

However, gasoline itself is typically available in three grades: standard, mid-grade and premium. But some gas stations even offer “E-15” and “E-85” grades, adding to the confusion at gas pumps.

First, let’s cover diesel, which is far less common than gasoline powered vehicles. Diesel is a higher viscosity (thickness) fuel, which is derived from crude or mineral oil produced by wells.  Burnt in engines designed specifically for diesel, it is consumed under extremely high compression and without additional combustion help from a spark plug. Diesel fuel is very efficient, delivering higher power under combustion and is most efficient when used in hot engines running for long periods of time. That is why it is used primarily in locomotives, tractors, semi-trucks and vehicles or equipment that have to run under high power for extended periods of time.

The use of diesel fuel has its drawbacks, which contributes to its limited use in passenger vehicles in the United States. Diesel engines tend to be noisy due to the high pressures under which they operate. Diesel fuel combustion also creates higher levels of soot and pollution, leading to additional steps necessary to retrofit the engines and exhaust systems to reduce pollution. Lastly, because of the heavier duty construction necessary to accommodate the operations of diesel engines, they are more expensive to manufacture and are more expensive to purchase than gasoline powered engines.

If you have selected a diesel-powered vehicle, it is likely that you have made a conscious decision to do so based on the benefits listed above. Most people who choose diesel are aware of the benefits and often operate their vehicles for long periods of time. Always use diesel fuel in diesel-powered vehicles. The vehicle will not operate on any gasoline variety and using gasoline will also cause substantial damage to the engine and/or its key operating systems (fuel pump, injectors, etc.)

Gasoline is much a thinner variety of engine fuel that is more refined and has higher explosive tendencies than diesel fuel. Like diesel, gasoline is derived from refining mineral oils pumped from wells drilled into the earth. Gasoline is typically available in three standard grades and there are now two newer ethanol-blend types: E-15 and E-85. There are two basic differences in these grades, one is the “Octane Rating,” the second is the amount of Ethanol blended into the fuel.

Octane is a measurement of the ability of fuel to burn efficiently and at the correct time within the combustion chamber of your engine. This essentially is a calculation based on chemical properties that most people would need an advanced science degree to understand, but the bottom line is it’s the fuel’s ability to burn without causing detonation -- or engine knock or “ping.”

So the basic difference between the three base grades of gasoline, standard, mid-grade and premium, is the octane rating. Standard grade gasoline has octanes in the range of 87, mid-grade is typically 88 or 89, with premium having an octane rating of 90 to 94. (There are also higher-octane ratings for specialty fuels, such as racing and jet fuel, but we won’t cover those.) 

Modern engines automatically adjust fuel ratios, engine timing and other factors to prevent detonation during operation. In order to prevent detonation, typically engines will run a bit richer or retard the timing. Both changes result in less efficient operation of the engine, which will reduce your engine’s ability to deliver full power and may slightly lower fuel mileage.

Due to the loss of efficiency, most manufacturers of high output or high-performance engines typically recommend using higher-octane mid-grade or premium fuel. If you own a Nissan 370Z, Nissan GT-R or similar high-performance vehicle, premium fuel is recommended for the best output of horsepower and full performance of your vehicle.

Despite this, most modern engines will and do run perfectly fine on standard grade gasoline, as they are designed and tuned for that grade of fuel. For example, the 2019 Nissan Altima models feature two, four-cylinder engine options, with even the powerful 2.0 Liter turbo four-cylinder option optimized for standard grade gasoline while delivering an EPA-estimated 25 miles per gallon (mpg) in city driving and 34 mpg on the highway. The 2.4 Liter non-turbo engine also runs efficiently on standard grade gasoline and delivers an impressive estimated 28 mpg in city driving and up to 39 mpg in highway driving.**

When it comes to filling up your tank, the choice is yours because all three grades offer full functionality in most gas engines. If you are an average driver and typically use your vehicle for modest driving or normal commuting and errands, standard grade fuel will work just fine. If you want to get the most performance out of your vehicle, if you are going to carry heavy loads or operate at higher speeds, you may want to use mid-grade or premium fuels.

Ethanol is a renewable fuel based on alcohol derived from plant material, typically corn, soybeans or sugar cane. Ethanol is very flammable and burns cleanly at a rapid rate and is typically used to raise the octane rating of gasoline. The biggest benefit to ethanol is reducing pollution because its clean-burning characteristics reduce soot and other noxious emissions.  Most modern gasoline is already blended with ethanol at rates up to 10%, and modern vehicles are designed to burn this blend without any damage to the engine or its peripheral systems.

The two newer ethanol blends (E-15 and E-85) have a much higher ratio of ethanol to gasoline, E-15 has a 15% blend of ethanol (hence the E-15 designation) and E-85 consists of 85% ethanol. These higher ratio blends of ethanol require more extensive changes to the engine and its peripheral operating systems (fuel pump, fuel injectors, computer sensors, etc.) due to the characteristics of ethanol. These modifications are only found on “Flexible Fuel” or flex-fuel vehicles and these E- blends should only be used in vehicles designated as such. However, all flex-fuel vehicles also run on any of the standard gasoline blends without causing any damage to the engine or its systems.

What Should You Do If You Put the Wrong Fuel In Your Vehicle?

So what happens if you accidentally put the wrong fuel in your vehicle? If you have a gas-powered vehicle and accidentally fill it with diesel (or vice-versa) you should NOT operate the vehicle because you could cause major damage. You will need to have the vehicle towed to an auto repair shop to have the fuel system drained and flushed.

If you inadvertently put one of the three standard grades of gasoline into your gas or flex-fuel vehicle, there should be no problem and you can drive it until your next fill and then change back to the correct grade of gasoline. (Note: If you used standard or mid-grade gas and you typically use premium, you may notice a slight decrease in your car’s performance.)

If you put either of the E-grade flex-fuels in your standard gasoline automobile, you may be able to operate it until your next fill or you may have to have the fuel system drained or flushed. If this occurs, contact your local dealership service department for more information and advice on what to do.

We always recommend that you consult your owner’s manual for the recommendation on the type and grade of fuel to use in your vehicle.

If you find that you need service or maintenance on your Nissan or other vehicle, Neil Huffman Nissan of Frankfort can help with your car repair needs. From oil changes to tire rotations, brakes, batteries and multi-point vehicle inspections, we can handle it all. 

  

* https://www.bts.gov/archive/publications/bts_fact_sheets/oct_2015/entire

** https://www.nissanusa.com/vehicles/cars/altima/performance.html