Best Fuel Options For Your Subaru Pressure Washer

Choosing the right fuel for your Subaru is essential for maintaining optimal engine performance and health. The correct fuel type varies depending on the specific Subaru model you own. For instance, the Subaru XV, Outback, and Forester are designed to run on 95 RON unleaded petrol, while the Impreza uses 91 RON unleaded petrol. On the other hand, the high-performance WRX and BRZ models require premium unleaded petrol with a higher RON of 98. It is crucial to use the recommended fuel type, as using a lower RON rating may cause engine knocking, and a higher RON may not provide additional benefits or even impact performance negatively.

Fuel types and their octane ratings

The octane rating of a fuel is a measure of its ability to resist 'knocking' or 'pinging' during combustion. Knocking or pinging is caused by the air and fuel mixture pre-igniting or detonating prematurely in the engine. The higher the octane rating, the greater the fuel's resistance to knocking.

In the US, there are three main grades of unleaded gasoline, distinguished by their octane ratings:

• Regular (87 octane)
• Midgrade (88-90 octane)
• Premium (91-94 octane)

Some regions sell gasoline with an octane rating of 85, which is suitable for older vehicles with carbureted engines in high-elevation areas.

Most gasoline vehicles are designed to run on regular 87 octane fuel, but some vehicles, especially those with high-compression engines, require higher octane fuel to prevent knocking and improve performance and fuel economy.

For example, Subaru's performance models, including the WRX, WRX STI, and BRZ, require premium fuel with an octane rating of 91 or higher. Using the correct octane fuel in these vehicles ensures optimal power and acceleration. On the other hand, using a lower octane fuel than required can cause the engine to run poorly and can damage the engine over time.

It is important to refer to the vehicle's owner's manual to determine the recommended octane level and use the correct fuel grade to prevent engine knocking and ensure optimal performance.

Recommended fuel for non-performance Subaru models

For non-performance Subaru models, such as the Crosstrek, Forester, Outback, Legacy, and Ascent, the recommended fuel is regular 87-octane fuel. These vehicles are designed to run efficiently on regular fuel, providing a good balance of performance, fuel economy, and cost savings.

Using a higher octane fuel in these models will not enhance performance or efficiency, so it’s best to stick with regular unleaded. Filling up with the wrong fuel type will negatively impact your engine and may even cause serious damage to other parts of your car, like the catalytic converter.

In Australia, the Subaru XV, Outback, and Forester are designed to run on 95 RON unleaded petrol. The Subaru Impreza drinks 91 RON unleaded petrol, and the Subaru BRZ and WRX are high-performance vehicles that require premium unleaded petrol fuel or 98 RON unleaded.

Recommended fuel for performance Subaru models

If you own a performance-oriented Subaru model, such as the WRX, WRX STI, or BRZ, your vehicle requires premium fuel with an octane rating of 91 or higher. These models are equipped with high-compression engines that benefit from the anti-knock properties of premium fuel.

While it is possible to use lower-octane fuel in a pinch, doing so may result in reduced performance and could potentially harm the engine over time. The WRX owner's manual states that fuel with an octane rating of 87 or higher can be used without detriment to engine durability, although there may be some slight degradation in performance. The WRX STI, on the other hand, requires 93 octane fuel, although the owner's manual states that 91 octane is acceptable if 93 octane is not available in your area.

It is important to note that using a higher octane fuel in a Subaru model that does not require it will not improve performance or fuel economy. For non-performance Subaru models such as the Crosstrek, Forester, Outback, Legacy, and Ascent, regular 87-octane fuel is perfectly adequate and provides a good balance of performance, fuel economy, and cost savings.

To summarise, for performance Subaru models, it is recommended to use premium fuel with an octane rating of 91 or higher to ensure optimal engine performance and avoid potential engine damage.

Why the right fuel grade matters

Using the right fuel grade for your vehicle is essential for optimal performance and engine health. Here's why it matters:

Prevent Engine Knocking

The octane rating of fuel indicates its ability to resist "knocking" or "pinging," which is caused by premature detonation of the air-fuel mixture in the engine. Engine knocking can lead to damage over time, and using the correct octane fuel helps prevent this issue.

Optimal Power and Acceleration

The right fuel grade ensures your engine delivers the intended power and acceleration. This is especially important for performance vehicles, where using a lower octane fuel can result in reduced performance.

Fuel Efficiency

Using a higher octane fuel than recommended does not improve fuel efficiency in vehicles designed to run on regular unleaded gasoline. It will only increase your fuel costs without providing any additional benefits.

Engine Health

Using a lower octane fuel than recommended can potentially harm the engine over time. In high-performance engines, this can lead to reduced performance and efficiency. Additionally, running a lower-grade fuel for an extended period can cause carbon build-up inside the engine, reducing efficiency and potentially leading to internal damage.

Manufacturer Recommendations

Always refer to your vehicle's owner's manual for specific fuel requirements. It will specify the recommended minimum octane rating for your vehicle. Following these recommendations ensures that your engine operates within the intended parameters and helps maintain its performance and longevity.

Fuel grade FAQs

No. Using premium fuel in a Subaru designed for regular unleaded gasoline will not improve its performance or fuel economy.

If you inadvertently use a lower octane fuel, your vehicle’s engine management system will adjust to prevent knocking. However, it’s best to refuel with the correct octane rating as soon as possible.

For vehicles designed to run on regular fuel, switching to premium occasionally is not harmful, but it is unnecessary. For performance models, consistently using the recommended premium fuel is important to maintain engine performance.

Top Tier gasoline has a higher concentration of additives and detergents beyond what is required by law. This keeps your engine cleaner and further reduces exhaust emissions.

E85, also called Flex Fuel, is made with 85% ethanol and 15% gasoline. However, this gas should only be used with Flex Fuel Vehicles. Adding it to an unequipped engine may cause problems with the vehicle's fuel system.

Diesel fuel is an oil that is a byproduct of the process that makes gasoline. Diesel fuel ignites under pressure without the need for a spark, and this fuel simply won't work in a gas engine.

Frequently asked questions