Can I put regular gas in a premium Lexus IS 350?
The short answer is no. The Lexus IS 350 is designed to run on premium unleaded gasoline (high-octane fuel), and using regular gasoline is not recommended. Always check your owner's manual for the exact octane specification, which in most markets is 91 AKI (or higher) in the United States and a higher octane in Europe and other regions.
What the IS 350 requires
The IS 350 uses a 3.5-liter V6 that benefits from higher-octane fuel to deliver the engine’s intended performance and efficiency. In the United States, the owner's manual typically specifies premium unleaded gasoline with an octane rating of 91 AKI or higher. In Europe and other regions, the equivalent guidance is usually a higher-octane rating such as 95–98 RON. The vehicle’s engine control system includes knock sensors that optimize timing to prevent knocking, but using fuel below the recommended octane can lead to reduced power and fuel economy.
Key octane guidelines for the IS 350:
- Premium unleaded gasoline with an octane rating of 91 AKI (or higher) is recommended in the US; higher octane is common in other markets.
- Regular gasoline (87 AKI in the US) is not recommended for daily driving in this engine and may cause the ECU to retune timing, reducing performance.
- Following the recommended octane helps preserve peak power and efficiency and aligns with warranty expectations.
In summary, the IS 350 is calibrated for premium fuel, and sticking to that specification supports the vehicle’s design, performance, and efficiency.
What happens if you use regular gas
If you accidentally fill with regular gasoline, you may notice diminished throttle response, slower acceleration, and lower peak power as the engine’s knock sensors retard timing to prevent detonation. The effect should lessen once you refuel with the proper premium octane, but prolonged use of lower-octane fuel can continue to impact performance and fuel economy until the engine readjusts.
Guidance for this situation:
- Do not rely on regular fuel long-term; refuel with premium at your next opportunity.
- Avoid heavy acceleration or towing when running on lower-octane fuel.
- Once you return to premium, the IS 350 should regain its normal performance and efficiency.
While the engine can operate on regular fuel in some circumstances, Lexus’s published guidance is to use premium to maintain optimal performance and to align with warranty expectations.
Regional variations and how to check your octane needs
Octane labeling and recommendations vary by region. In the United States and Canada, premium gasoline with 91 AKI or higher is typically specified. In Europe and other markets, octane is often listed as RON, with recommended figures commonly in the mid-90s (95–98 RON). Always consult your specific model year’s owner’s manual and the fuel label inside the fuel filler door for the exact specification applicable to your car.
Tips to verify the correct fuel for your vehicle:
- Check the owner’s manual for the exact octane specification for your year and region.
- Look at the fuel filler door label, which often repeats the recommended octane rating.
- When in doubt, choose premium gasoline and avoid regularly using lower-octane fuel.
If you’re traveling internationally, plan ahead to ensure you have access to the required octane level, as regional variations can be significant.
Summary
The Lexus IS 350 is designed to run on premium unleaded gasoline with an octane rating of 91 AKI or higher (or the regional equivalent). Regular gasoline is not recommended and can lead to reduced performance and efficiency as the engine adapts timing to prevent knocking. Always refer to your owner’s manual or fuel door sticker for the exact specification relevant to your model year and market, and refuel with premium to maintain the vehicle’s intended performance.
