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Can you put regular gas in Lexus IS 350?

Yes, you can physically pour regular gasoline into a Lexus IS 350, but it is not the recommended fuel for normal driving. The IS 350 is engineered for premium unleaded fuel (typically 91 octane or higher) to deliver its designed performance, and using regular may reduce power and efficiency, with the car’s engine management compensating by retarding timing if needed.

Fuel requirements for the IS 350

Understanding octane and what Lexus recommends helps owners make informed fueling choices.

Recommended fuel: Premium unleaded gasoline with an octane rating of 91 or higher. This is stated in the manuals for many IS 350 models to ensure optimal performance and efficiency.

Regular gasoline (87 octane): The vehicle’s knock sensors will detect pre-ignition and may cause the engine to adjust timing. This can result in reduced power, slower acceleration, and lower fuel economy during normal driving.

Emergency use: If you must refuel with regular gasoline in a pinch, it is generally advised to refill with premium at the next opportunity to restore optimal performance and avoid prolonged knock risk.

In short, while regular gas can be used temporarily, the IS 350 is designed with premium fuel in mind. Prolonged use of lower-octane fuel can compromise performance and efficiency and may lead to engine knocking under certain driving conditions.

Model-year and market variations

Fuel specifications can vary by model year and market, so it’s important to consult your specific owner’s manual for exact guidance. In most regions, Lexus recommends premium unleaded gasoline, with 91 octane or higher being the common standard to achieve the advertised power output and smooth operation.

United States and Canada

For U.S. and Canadian IS 350 models, premium unleaded gasoline (91 octane or higher) is typically the recommended option to maintain performance and emissions characteristics. Regular unleaded gasoline may be used only if the manufacturer’s manual explicitly allows it for a given year, and drivers should expect a reduction in performance when it is used regularly.

Europe and Asia

In Europe and parts of Asia, octane ratings are often expressed as RON (for example, 95–98 RON). Even so, IS 350 owners are usually advised to use higher-octane premium fuels to preserve engine performance and smooth operation. Always check the local manual, as regional variants can differ in octane requirements.

Practical guidance for fueling decisions

If you’re weighing fueling options, consider these guidelines to minimize risk and maintain engine health.

Keep to the recommended octane: Use premium gasoline (91 octane or higher) as specified by your model year and market.

Avoid habitual use of regular gas: Frequent use of 87 octane can lead to reduced power, higher engine temperatures, and lower efficiency.

In an emergency: If you accidentally fill with regular gas, drive conservatively and refuel with premium at the next opportunity. Avoid aggressive driving until you’re back on premium fuel.

Following the recommended octane helps ensure the IS 350 operates as designed, preserves performance, and maintains fuel economy over time.

Summary

The Lexus IS 350 is best fueled with premium unleaded gasoline (91 octane or higher) to preserve its intended performance and efficiency. Regular 87 octane is not recommended for normal use and may trigger timing adjustments that reduce power. If regular gas is used only temporarily, refuel with premium as soon as possible. Always verify the exact requirement in your vehicle’s owner’s manual, as specifications can vary by year and market.

What happens if I put 87 instead of 91?

If you put 87 octane instead of 91 in a car that requires it, your modern engine's computer will likely adjust timing to prevent damage, but you may experience reduced performance and fuel efficiency. For a one-time mistake, drive gently and fill up with 91 octane the next time to dilute the fuel. However, consistently using lower-octane fuel in a high-compression or performance engine can lead to engine knocking and potential damage.
What to expect in the short term

Reduced performance: You may notice less acceleration and overall power.
Engine knocking or pinging: This is a rattling noise that can occur when the fuel pre-ignites in the cylinder.
Decreased fuel economy: Your car may use more fuel to go the same distance.

How to mitigate the effects

Avoid hard acceleration: Drive gently, especially at high speeds or when climbing hills, to minimize the risk of engine knocking.
Fill up with 91 octane: When your fuel tank is low, fill it up with 91 octane to mix with the remaining 87 octane fuel. This will dilute the lower-octane fuel and raise the overall rating.
Check your owner's manual: The manual will specify if 91 octane is a requirement or simply a recommendation.
Be cautious with performance vehicles: Cars with turbochargers or high-compression engines are more susceptible to damage from lower-octane fuel, so it is especially important to avoid aggressive driving.

Should you put premium gas in a Lexus?

Whether a Lexus requires premium gas depends on the specific model and year. Many higher-performance and luxury models, like the IS, LS, and RC series, require premium fuel, while other models, such as the ES and some UX and NX versions, run on regular unleaded. It is best to check your owner's manual to determine the correct fuel type for your vehicle, as using the wrong type of gas in a model that requires premium could lead to engine damage and void your warranty.

Lexus models that typically require premium gasoline

Lexus IS (IS 300, IS 350, IS 500)
Lexus LS (LS 500, LS 500h)
Lexus RC (RC 300, RC 350, RC F)
Lexus LC (LC 500, LC 500h)
Lexus RX (RX 350, RX 450h)
Lexus NX 350 and NX 450h+

Lexus models that typically use regular unleaded

Lexus ES (ES 250, ES 350, ES 300h)
Lexus UX 200
Lexus NX 250

Important considerations

Check your owner's manual: Always consult your owner's manual for the most accurate information for your specific vehicle.
Engine damage: Using regular gas in a vehicle that requires premium could potentially damage the engine and may void your warranty.
Performance: Premium fuel is designed to help high-performance engines operate at their optimal level, but using premium in a car that only requires regular will not provide any performance or efficiency benefits.

Which Lexus can run on regular gas?

Several Lexus models use regular 87-octane gasoline, including the Lexus ES (e.g., ES 250, ES 350, ES 300h) and the UX 250h. Some NX models like the NX 250 (for example, the 2024 and 2025 models) also use regular gas. It is essential to check your specific model's owner's manual for the correct fuel recommendation.
Models that use regular gas

Lexus ES: Models like the ES 250, ES 350, and ES 300h are designed to run on 87-octane regular gasoline.
Lexus UX: The UX 250h, such as the 2024 model, uses regular gas.
Lexus NX: Some NX models, such as the 250, use 87-octane regular fuel.

Important considerations

Consult your owner's manual: The most accurate information for your specific vehicle will always be in the owner's manual.
Premium is required for some models: Many other Lexus models, especially performance-oriented or turbocharged ones like the IS, GS, LS, and some RX, RC, and LX versions, require a minimum of 91-octane premium fuel.
Consequences of using the wrong fuel: Putting regular gas in a car that requires premium can potentially cause engine damage over time.

What will happen if I put regular gas in my Lexus?

If you put regular gas in a Lexus that requires premium, you may experience reduced engine performance and hear engine knocking, especially under heavy acceleration. While a one-time mistake likely won't cause lasting damage, consistently using regular gas can lead to long-term engine problems over time. Check your owner's manual to confirm if your specific Lexus model actually requires premium fuel, as some models are designed to run on regular gas.
Potential effects of using regular gas

Reduced performance: You may notice a decrease in power and acceleration.
Engine knocking: The engine may "knock," which is a harsh metallic sound caused by premature or uneven combustion. Consistently ignoring this can lead to engine damage.
Engine damage: Over time, continuous use of regular gas in an engine designed for premium can cause serious, long-term damage.

What to do

Check your manual: First, consult your car's owner's manual to see if your model genuinely requires premium gas. Many Lexus models, especially certain SUVs and hybrids, are designed to run on regular 87-octane fuel without issue.
If you accidentally used regular: If your car requires premium but you've put regular in, don't panic. It's best to avoid hard acceleration or heavy driving until you can top off the tank with premium fuel. Your car's computer will adjust the engine timing to compensate for the lower octane, preventing damage from a single fill-up.
If you consistently use regular (when premium is required): This is when you risk serious engine damage. The long-term effects of engine knocking and underperformance can lead to costly repairs.

Kevin Bennett

Company Owner

Kevin Bennet is the founder and owner of Kevin's Autos, a leading automotive service provider in Australia. With a deep commitment to customer satisfaction and years of industry expertise, Kevin uses his blog to answer the most common questions posed by his customers. From maintenance tips to troubleshooting advice, Kevin's articles are designed to empower drivers with the knowledge they need to keep their vehicles running smoothly and safely.