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Types Of Gas A Kia Optima / K5 Takes (All Generations)

Types Of Gas A Kia Optima / K5 Takes (All Generations)

On this blog, we conduct extensive research into specific questions about various automobiles. Today, we’ll look at the American-made Kia Optima / K5 and see what kind of gas it needs.

We looked through the owner’s manuals of Kia Optima / K5 from 2009-2021 to find out the best-recommended gas for the car, as well as a detailed analysis of the engine, mileage, and tank capacity of various Kia Optima / K5 models by year.

So, what type of gas does a Kia Optima takes?

All Kia Optima / K5 are designed to use high-quality unleaded regular gasoline with an octane rating of 87. The use of premium fuel with an octane of 91 or higher is not recommended since this will have no benefit for the Optima / K5.

However, this does not tell the complete specs. In this article, we will delve into the specifics of the Kia Optima and provide you with information on Kia Optima gasoline types and which gas is good or bad for the durability of your engine and performance. We’ll also discuss tank size and the cost of filling the tank in various states.

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Infographic explaining the different fuel types for a Kia Optima (K5)

Fuel Requirement Based On Engine Type

In this section, we will look over the various engine options available in the Kia Optima / K5 models and the best type of gas to use with them.

2021 – Present

The standard engine in the 2021 Kia K5 is a 1.6-liter turbo four-cylinder engine with 180 hp and generates 195 pound-feet of torque, mated to an 8-speed automated transmission. For the new model year, it may also be available with an all-wheel-drive system. The 2021 K5 GT is powered by a 2.5L turbo four-cylinder engine pushing out 290-hp with 311 lb-ft of torque.

2016 – 2020

Kia Optima from 2016-2020 comes with a standard 185-horsepower 2.4-liter four-cylinder and S6 automatic transmission. Two turbocharged options are available. The EX trim features a 1.6-liter turbo-four rated at 178 horsepower mated to an S7 dual-clutch automatic transmission. The top-of-the-line SX gets a 2.0-liter turbo-four that produces 245 horsepower paired to S6 automatic transmission.

Similarly to other Kia models like the Kia Forte for instance, Kia Optima, Kia Optima FE, Kia Optima hybrid from 2016-2020 prefer the use of regular unleaded gasoline with an octane rating of 87 or higher.

2012 – 2015

The 2012-15 models of Kia Optima have a 2.4-liter four-cylinder engine that makes 192 hp. A 274-hp, turbocharged, 2.0-liter four-cylinder engine is available in higher trims. Both engines are made to use a six-speed automatic transmission and are suitable for people looking for V6-like power.

It’s engineered to obtain maximum performance with unleaded gasoline while reducing exhaust pollutants and spark plug fouling. Never use any fuel system cleaning products other than those recommended by the manufacturer in the fuel tank.

2009 – 2011

The 2011 Kia Optima has a 2.4-liter four-cylinder generating 200-hp, a 2.0-liter turbocharged four-cylinder engine that produces 274-hp, and a hybrid model, which is also recommended to use octane rating of 87 and regular unleaded gasoline.

What Types Of Gasoline Can And Can’t Be Used?

When filling up your tank, you’re bound to see different types of gasoline at the pump, and it’s essential to choose your gasoline option wisely.

After all, not all gases are created equal. Some octane levels, which we will discuss later, are appropriate for one car but not another. So read onto know about the different gasoline types so you can choose the suitable gas for your vehicle.

Gasoline Containing Alcohol or Methanol

Gasohol (also known as grain alcohol), a blend of gasoline and ethanol and gasoline or gasohol with methanol (also known as wood alcohol), are offered alongside or in place of leaded or unleaded gasoline.

In the owner’s manual of Kia Optima, it is recommended to use only gasoline or gasohol that contains less than 10% ethanol. A fuel made up of 90% regular unleaded petrol and 10% ethanol is called E10. It results in lower emissions in the vehicle.

Ethanol contains approximately 35% oxygen and burns cleaner than gasoline. E10 fuel has been shown to reduce fuel emissions by up to 30%, so it is a safe and dependable fuel that will not damage your vehicle. It’s also a lot cheaper to buy than regular gasoline.

Using gasohol containing more than 10% ethanol or gasoline containing any methanol can damage the fuel system and cause drivability issues. If you experience drivability issues, stop using gasohol of any kind.

Vehicle damage or drivability issues may be excluded from the manufacturer’s warranty if they are caused by the use of:

  1. Ethanol-containing gasoline that contains more than 10% ethanol.
  2. Methanol-containing gasoline or gasohol.
  3. Leaded gasoline or leaded gasoline.

E85 (Ethanol) Fuel

E85 fuel is an alternative fuel made up of 85% ethanol and 15% gasoline designed exclusively for use in Flexible Fuel Vehicles.

“E85” is incompatible with Kia Optima and all its models. Using “E85” may result in poor engine performance and damage to your vehicle’s engine and fuel system. Ethanol is hygroscopic in nature; It is corrosive to fuel-system components such as magnesium, aluminum, rubber, and other non-metallic elements.

As ethanol attracts water, it can cause rust and seal breakage over time. If E85 is left in the fuel tank for an extended period of time, it can attract more water vapor and potentially destroy the engine and fuel system in a short period.

It’s susceptible to pre-ignition. Due to the ethanol component in E85, it’s more likely to ignite before the piston compresses and the spark plug does its job.

Another reason is E85 has octane readings between 89 to 105, while the octane rating recommended for Kia Optima is 87. Using higher octane of premium gas won’t make your car faster; in fact, the opposite is possible as higher-octane fuel technically has less energy than lower-octane fuel.


Kia Optima Limited Warranty does not accommodate fuel system destruction or performance issues caused by “E85” fuel.

MMT-Fortified Gasoline

Some gasoline contains dangerous manganese-based fuel additives, such as MMT (Methylcyclopentadienyl Manganese Tricarbonyl). Kia does not recommend MMT-containing gasoline.

Long-term use of MMT will result in the accumulation of Mn-containing deposits on the engine and increased emissions of HC, CO, NOx, catalyst plugging, resulting in deteriorated performance and durability of the engine.

The health consequences and costs of using MMT as a gasoline additive would include both direct manganese emissions. These traditional pollutants have been linked to health effects such as premature death, asthma, and cardiopulmonary diseases.

The Canadian federal government passed legislation (C-29) prohibiting interprovincial trade and commercial importation of manganese-based substances, including MMT. As a result, as much as 95% of Canadian gasoline is now MMT-free.

Therefore the use of MMT is detrimental, and it can impair vehicle performance and interfere with your emission control system. On the cluster, the malfunction indicator lamp may illuminate.


MTBE is a highly hazardous chemical that can harm both animals and humans in various ways. An unresolved problem is a role played by MTBE metabolites, especially tertiary Kia recommends avoiding MTBE (Methyl Tertiary Butyl Ether) fuels containing more than 15.0 percent vol. (Oxygen Content 2.7 percentage) in your vehicle.

Since MTBE is not soluble in water, if fuel containing MTBE leaks from an underground storage tank at a gas station, it can contaminate the groundwater and the wells’, eventually, the surface water, furthermore, while MTBE reduces the amount of most pollutants emitted by automobiles, it also emits a harmful pollutant, formaldehyde.

MTBE has been banned in many states in the US in exchange for its most common alternative, ethanol, which shows signs that MTBE is harmful to the car’s engine and can cause problems to the durability of the engine of your Kia Optima.

Fuel Additives

KIA recommends using gasoline-containing detergent additives designed to make your engine perform smoothly by preventing gunk or trace deposits from forming in the car’s engine to make a significant contribution to cleaner air. It can also aid in the removal of existing build-up.

These fuel additives avoid sluggish acceleration, rough idling, cold-start issues, stalling, and stumbling. They play an essential role in reducing deposits on the automobile’s combustion chamber and valves of Kia optima.

This gasoline will allow the engine to run cleaner and the Emission Control System to work more efficiently. You can actually increase your MPG simply by using a fuel additive. TOP TIER gasoline keeps internal engine components up to 19 times cleaner than gasoline that meets minimum EPA standards.

For additional details, go to TOP TIER Detergent Gasoline. Additives that can be purchased separately may be added to the gasoline for customers who do not regularly use TOP TIER Detergent Gasoline and have difficulty starting or running the engine smoothly.

If Detergent Gasoline is not available, one bottle of additive should be added to the fuel tank every 7,500 miles or every engine oil change. Information on how to use the Additives is available at your authorized Kia dealer. Other additives should not be combined.

What If I Hear A Knocking Noise From The Engine After Refilling?

If your Kia Optima starts making strange noises out of nowhere, you should be concerned. These noises frequently indicate a problem with your Kia that will need to be repaired. However, if you hear sounds coming from your car’s engine, you should be especially concerned.

Here’s a video talking in more detail about engine knocking:

You might listen to engine knocking when your vehicle is idling, revving your engine, or when you’re going at a fair speed down the street.

Thus engine knocking has to be addressed, or it can lead to significant problems for Kia owners in the future.

  1. The problem could be caused by the fact that you’re driving on fuel with a considerably lower octane level than you should be.
  2. Due to the carbon built up inside of your car’s engine cylinder.

If you hear the noise, the consensus is that you should pull over immediately and contact a garage or nearby dealership before it becomes a significant issue.

Does The Kia Optima Have A Good Gas Mileage?

2016 – 2021

The Optima’s turbocharged 1.6-liter engine gets 27 mpg in the city and 37 mpg on the highway. Optima’s turbocharged 2.0-liter engine returns 22 mpg in the city and 31 mpg on the highway and has a combined MPG of 25.

Kia Optima Hybrid 2.0L gasoline engine has a city MPG of 39, highway MPG of 46, and a combined MPG of 42. The Optima’s base 2.4-liter engine gets 25 mpg in the city and 35 mpg on the highway with a combined MPG of 29. The 2.5L gasoline engine has a city MPG of 24, a highway MPG of 32, and a combined MPG of 27.

1.6L S6273731
1.6L S8293832
2.0L Hybrid394642

2009 – 2015

According to the EPA, the four-cylinder, 2.0L gasoline engine Optima gets 22 mpg in city driving and 33 on the highway, having a combined mpg of 26.

Optima with the base 2.4L gets34/38 mpg city/highway with a combined mpg of 36 while models with 2.7L 6 cylinder have 20/28 mpg city/highway with a combined mpg of 23.

2.7L 6-cyl202823

What Is The Gas Tank Size Of Kia Optima?

The American-made Kia Optima from 2016-2021 with a 2.0L and Kia Optima AM7, 1.6L engine has a tank size of 18.5 gallons. Kia Optima plug-in hybrid has a 14.5-gallon tank size. The 2.4L AM6 engine has a 17.2 to 18.5-gallon tank size. A 2.0L AM6 engine of the optima hybrid has a tank size of 15.9-gallons.

While the 2010 Kia optima come with an engine of 2.4L and 2.7L, have a tank capacity of 16.4 gallons.

How Much Does It Cost To Fill Up A Kia Optima?

On average, it will cost up to $60 to fill up Kia Optima with an 18.5-gallon tank size produced from 2012 to 2021. And it will cost up to $47 (gas only) to fill up the tank size 14.5 gallons of optima plug-in Hybrid. Also, for the 2010 Kia Optima with a 16.4 gallons tank size, it will cost up to 54$ only while 56$ for a 17.2 gallons tank.

Filling your tank in California will be the costliest, will cost you around $68 to $87 depending on the tank size, and Oklahoma is the cheapest state for filling the tank; it will cost you an average of $45 to $57 again, depending on the models and the tank size.

Closing Thoughts

Fueling your Kia Optima / K5 with the right type of gas is not just a matter of performance; it’s a matter of preserving the longevity and efficiency of your vehicle. As we’ve learned the Kia Optima is engineered to perform optimally with unleaded regular gasoline with an octane rating of 87.

For those interested in further exploring the durability of Kia models, consider reading “How Many Miles Can A Kia Forte Last“, a comprehensive look at the longevity and common issues of the Forte, or “How Many Miles Can A Kia Sedona Last“, where we dissect the life expectancy of Kia’s spacious minivan.

Remember, knowing your car’s needs is akin to understanding a close friend—it results in a long, harmonious relationship. Happy driving!


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