Subaru Ascent 2018-2026 Owner's Manual: Fuel requirements

The Subaru Ascent engine is engineered to operate efficiently on unleaded gasoline with an octane rating of at least 87 AKI (90 RON). Using the correct fuel ensures optimal performance, fuel economy, and engine longevity.

NOTE

When towing with the Subaru Ascent, it is advisable to use higher-octane fuel (91 AKI / 95 RON or above). This helps reduce the risk of engine overheating and ensures stable performance under increased load conditions.

Fuel octane rating

Using fuel with an octane rating lower than recommended may cause engine knocking. Occasional light knocking during acceleration or uphill driving in the Subaru Ascent is normal; however, persistent or severe knocking should not be ignored and requires inspection by a SUBARU dealer.

RON

The Research Octane Number (RON) is a standard measure of fuel performance under controlled conditions.

AKI

The Anti-Knock Index (AKI) represents the average of the Research Octane Number and the Motor Octane Number, and is the commonly used rating in many regions for fuels suitable for the Subaru Ascent.

Unleaded gasoline

The Subaru Ascent fuel filler neck is specifically designed to accept only unleaded gasoline nozzles. Using leaded fuel is strictly prohibited, as it can damage the emission control system, reduce fuel efficiency, and impair overall vehicle performance.

Reformulated gasoline

Subaru supports the use of reformulated gasoline, which is designed to burn cleaner and reduce harmful emissions. Using such fuel in the Subaru Ascent contributes to improved environmental performance.

MMT

Some fuels contain an additive known as MMT (Methylcyclopentadienyl Manganese Tricarbonyl), used to increase octane rating. However, prolonged use in the Subaru Ascent may lead to reduced emission system efficiency and may trigger the CHECK ENGINE warning light.

If such a condition occurs, consult an authorized SUBARU dealer. If the issue is caused by fuel type, repairs may not be covered under warranty.

Gasoline for cleaner air

Using high-quality gasoline with detergent additives helps prevent carbon deposits in the Subaru Ascent engine and fuel system. This ensures smoother operation, maintains engine efficiency, and supports proper functioning of emission control components.

Modern fuels often include oxygenates such as ethanol, which help reduce emissions. The Subaru Ascent is compatible with gasoline containing up to 15% ethanol (E15).

Do not use fuels with ethanol content exceeding 15%, such as E30, E50, or E85, as they are not suitable for the Subaru Ascent and may cause damage to the fuel system.

If uncertain about fuel composition, consult the fuel provider to confirm whether the gasoline contains appropriate additives and meets Subaru Ascent specifications.

For reliable operation, always follow these recommendations:

• Use only unleaded gasoline with the specified minimum octane rating for the Subaru Ascent.
• Methanol (wood alcohol) may be present in small amounts.

  Methanol can be used ONLY if it does not exceed 5% of the fuel mixture and includes proper co-solvents and corrosion inhibitors. Avoid fuels exceeding this concentration.

• If drivability issues arise, try a different brand of gasoline before seeking service.
• Damage caused by improper fuel usage is not covered under the Subaru Ascent warranty.

CAUTION

Avoid spilling fuel on the exterior surfaces of the Subaru Ascent, as it may damage the paint finish.

If fuel is spilled, wipe it off immediately to prevent permanent damage. Paint damage caused by fuel is not covered under warranty.

The Subaru Ascent fuel system is designed for efficiency, durability, and environmental responsibility, but proper fuel selection remains essential for maintaining peak performance and long-term reliability.