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The Types Of Gas A Subaru Legacy Takes (Explained)

The Types Of Gas A Subaru Legacy Takes (Explained)

Today we are looking at Subaru Legacy, a Japanese mid-sized car, first produced in 1989 and now in its seventh generation in North America. We will provide a detailed analysis of the manufacturer’s recommendations on fuel types, fuel economy, tank size, and much more, but first, let us briefly summarize its fuel requirement.

All generations of the Subaru Legacy use regular, unleaded gasoline with an octane of 87. Only 2.5L engines for the 2005 – 2014 GT trim require premium, unleaded gasoline with an octane of 91 or higher.

In the rest of this blog, we will review each of the seven generations of Legacy from the perspective of the engine’s capacity, the type of recommended fuel, which fuel to use and which not to use, and a lot more. Hopefully, you will get to know Subaru Legacy better from its fuel economy perspective and compare it to other similar mid-sized cars by the end of it.

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Infographic explaining the fuel types for a Subaru Legacy.

Fuel Requirements Based On Engine Type

The Subaru is in its seventh generation of production in North America, and all run on unleaded gas, mostly regular. Still, some are required to run on premium gas as well. Starting with the first generation, we will look at all the engines and fuel types needed.

Also read: The Absolute Best Year Of The Subaru Legacy

First-generation (1990-1994)

For the North American market, Subaru introduced the Legacy with a 2.2L engine that ran on regular unleaded fuel with an octane of 87.

Second generation (1995-1999)

The second generation was marked by introducing a 2.5L engine in 1996 that used regular unleaded fuel with an octane of 87. The 2.2L was also carried over from the previous generations, which were also based on regular unleaded fuel with an octane of 87. 

Third generation (2000-2004)

Subaru used a 2.5L engine for all Legacy trims for the third generation. These engines were based on regular unleaded fuel with an octane of 87.

Fourth generation (2005-2009)

For the fourth generation, Subaru introduced two engine-related changes for the Legacy. A 3.0L engine was introduced that used regular unleaded fuel with an octane of 87. The other change was the introduction of 2.5L engines for the GT trims that ran on premium unleaded fuel with an octane of 91. All other 2.5L engines were based on regular unleaded fuel with an octane of 87.

Also read: Subaru Legacy Transmissions: Overview, Problems, Fluids

Fifth-generation (2010-2014)

Subaru replaced the 3.0L engine with the 3.6L engine based on regular unleaded gasoline with an octane of 87 for the fifth generation. Besides, there were two versions of 2.5L engines based on regular unleaded and premium unleaded gasoline.

Sixth generation (2015-2019)

Most of the Legacy’s sixth-generation trims are based on a 2.5L engine, while a few also have a 3.6L engine under the hood. All are based on regular unleaded gasoline with an octane of 87.

Seventh generation (2020-present)

Legacy discontinued the 3.6L engine for the seventh generation and instead introduced a 2.4L engine to go along with the 2.5L engine. Both the 2.4L and 2.5L engines are based on regular unleaded gasoline with an octane rating of 87. This is the same type of gas that the Subaru Crosstrek takes.

Also read: The Exact Bolt Pattern Of A Subaru Legacy

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

All engines are designed to optimally run on a particular gas type identified by the octane rating. Most of us are aware of the term, but only a few understand it for what it is. Octane rating, also known as an anti-knock rating, measures how much the air/gas mixture in the cylinder of the internal combustion engine can be compressed before it detonates.

The higher the octane rating, the higher the pressure the mixture can withstand and the bigger the detonation. It means more heat energy is available for conversion into mechanical energy. Most of today’s cars are optimized to run on regular unleaded fuel.

However, performance car engines, such as turbochargers, require high octane premium gas for optimal performance and fuel efficiency. Using premium unleaded fuel when regular unleaded is recommended will only bite into your wallet without giving any engine performance benefits.

Reformulated Gasoline

Growing concerns over the air quality we breathe resulted in recommendations and reforms that led to the 1990 Clean Air Act amendments. Petroleum producers reacted to it by coming up with clean-burning fuels, the Reformulated gasoline (RFG).

It is a gasoline blend that burns more cleanly than conventional gasoline and helps to reduce smog-forming and toxic pollutants in the air we breathe. Subaru recommends the use of reformulated gasoline in its vehicles.

Gasoline/Oxygenated Blends Or E-85

Subaru allows the use of an oxygenated blend of gasoline for clean air. Examples of such fuels are MTBE (Methyl Tertiary Butyl Ether) or ethanol (ethyl or grain alcohol). The recommendation is that such fuels contain no more than 15% MTBE or 10% ethanol for the proper operation. 

Subaru does not recommend using gasoline that has more than 10% ethanol; examples of such fuels are those labeled as E15, E30, E50, or E85, all of which contain more than 10% ethanol. E85 or Flex fuel is also not recommended since ethanol is between 51%-83%.

Also read: Subaru Legacy Towing Capacity: Can It Tow A Trailer, Boat, Or Jet Ski?

Gasoline With Added Materials

Subaru also allows clean-burning gasoline with detergent additives that help prevent deposit buildup on engine and fuel systems. Such fuels are instrumental in keeping the engine healthy and the emission control system working efficiently. One of the most popular gasoline with added materials and detergents is TopTier gasoline. 

Subaru notes that continuous use of high-quality fuel with proper detergent and additives will ensure that there would be no need to use system cleaning agents. The use of prohibited fuel can cause damage to the engine and emission control systems and may lead to the warranty becoming void.

Gasoline With MMT

Some gasoline contains an octane enhancer additive called Methylcyclopentadienyl Manganese Tricarbonyl (MMT). The opinion is divided on the usage in vehicles, with some studies pointing to the detrimental effects on emission systems and spark plugs.

Subaru does not recommend using MMT as it may affect the emission control system’s performance and cause the CHECK ENGINE warning light/Malfunction indicator lamp to turn on. If that happens, you should have your Legacy checked and serviced by an authorized Subaru dealer.

If it is determined that the use of prohibited fuels causes the condition, then the repair may not be covered by warranty.

Also read: How Many Miles Can A Subaru Legacy Last? (Answered)

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

Knocking is a “pinging” sound produced because of the uneven burning of fuel in the engine’s combustion chamber. The cylinders must have a correct balance of air and fuel to maximize torque. When this happens, the fuel burns in small, regulated pockets and not all at once.

On the other hand, uneven burning of fuel leads to engine knocking. The effects of engine knock could range from inconsequential to devastating; therefore, it is crucial to identify the cause of knock. Consistent gasoline use with lower than recommended octane content can lead to engine damage and should be avoided.

There should not be any cause of concern if the engine sometimes knocks going uphill or accelerating. However, if the knock is persistent and appears to be getting worse, it is recommended to consult an authorized Subaru dealer.

Does the Subaru Legacy Have Good Gas Mileage?

In this section, we will tabulate the fuel economy data for the various engines used by Subaru to power the Legacy. We will give figures for the 2WD version. The values for AWD are about 1 MPG lower.

Furthermore, 2.5L GT engines have lower fuel economy compared to other 2.5L engines. The table contains fuel economy values for city, highway, and combined in MPG. Please note that the combined MPG is a weighted average of 55% of City MPG and 45% of highway MPG.

First-generation (1990-1994)

EngineCombined MPGCity MPGHighway MPG

Second generation (1995-1999)

EngineCombined MPGCity MPGHighway MPG

Third generation (2000-2004)

EngineCombined MPGCity MPGHighway MPG

Fourth generation (2005-2009)

EngineCombined MPGCity MPGHighway MPG

Fifth generation (2010-2014)

EngineCombined MPGCity MPGHighway MPG

Sixth generation (2015-2019)

EngineCombined MPGCity MPGHighway MPG

Seventh generation (2020-Present)

EngineCombined MPGCity MPGHighway MPG

What’s The Gas Tank Size Of the Subaru Legacy?

Subaru Legacy started with tank sizes of 14.8 and 15.9 gallons. In 1991, 15.9 gallons became the standard tank size until the second generation. Beginning with the third generation, Subaru changed the tank size to 16.9 gallons, and since the fifth generation, the tank size stands at 18.5 gallons.

How Much Does It Cost To Fill Up Subaru Legacy?

In the United States, as of 1/29/2022, the current average price of regular unleaded fuel is $3.361, whereas it is $3.988 for premium unleaded gas. Based on this, and for the tank sizes mentioned above, it would cost anywhere from $49.74 (14.8-gallon tank) to 62.18 (18.5-gallon tank) for regular unleaded fuel. Premium unleaded gas would cost between $67.40 (16.9-gallon tank) and $73.78 (18.5-gallon tank).


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