Can you mix 87 and 91 gas?
You can physically mix 87 and 91 gasoline, and the resulting octane will land somewhere between the two numbers depending on the blend. However, you should prioritize the octane your vehicle requires and not rely on mixing as a way to boost performance.
What octane means for engines
Octane rating measures a gasoline’s resistance to knocking, a pre-ignition phenomenon that can damage engines if unchecked. Vehicles with higher compression ratios, turbochargers, or performance tuning may require higher octane to prevent knocking. In the United States, the posted octane numbers on pumps reflect an AKI (anti-knock index) rating, which is used to guide fuel choice for most consumer vehicles.
Mixing 87 and 91: practical implications
Here are the key points to consider when blending these two octane grades in a tank.
- Blended octane will typically fall between 87 and 91, depending on how much of each fuel you mix and their specific formulations.
- For most cars designed to run on 87 AKI regular, adding some 91 does not reliably increase performance or fuel economy; the engine may simply operate with the same timing and power as before the blend.
- Engines with knock sensors and modern engine management can adapt to different octane levels, but using higher octane than the manufacturer requires generally offers limited or no noticeable benefits.
- Fuel blends may differ in ethanol content. Mixing fuels with different ethanol percentages can affect fuel stability and compatibility over time, especially if one fuel is ethanol-free and the other is not.
- Storage and long-term stability can be affected if fuels with different properties are stored together, particularly in warm climates or when the tank sits for extended periods.
In summary, mixing 87 and 91 is technically possible and will produce an in-between octane. It is not a reliable method to gain power or stopping safety margins beyond what your engine actually needs. Always use the octane grade recommended by your vehicle’s manufacturer.
Ethanol content and compatibility
Most gasoline sold in the United States contains ethanol (commonly E10, about 10%). Some regions offer non-ethanol options or different blends. Ethanol content can interact with fuel stability and water absorption, and mixing fuels with different ethanol levels may introduce slight variability in performance. If your vehicle is sensitive to ethanol content, check labels or consult your owner’s manual for guidance.
Practical guidance for vehicle owners
To minimize risk and avoid fueling mistakes, consider these guidelines.
- Always follow the octane grade specified in your owner's manual or on the fuel door sticker.
- If you accidentally fuel with a lower octane than recommended, avoid high-load driving until you can refuel with the correct grade; persistent knocking should be addressed by using a higher octane fuel.
- Using a higher octane than required is generally safe but may not improve performance or efficiency in most engines; benefits are typically limited to engines designed for higher compression or forced induction.
- Be mindful of ethanol content if your vehicle has sensitivities to ethanol or if you’re using non-standard fuel blends.
Bottom line: blending fuels is not a reliable way to improve performance. Stick to the octane your car requires and only consider higher octane if your engine calls for it or if you notice knocking under load.
Summary
Mixing 87 and 91 gasoline is physically possible, and the resulting octane will lie between the two numbers. For most vehicles, there is little to no benefit from mixing higher-octane fuel into regular fuel; engines designed for regular gasoline will not see meaningful performance gains. Always prioritize the octane recommended by your vehicle’s manual, and be aware of ethanol content and fuel stability considerations when mixing fuels. If in doubt, consult your vehicle manufacturer or a trusted mechanic.
What happens if you mix 87 and 91 gas on Reddit?
Nothing will happen. Unless it's somehow cheaper than 87 octane you're wasting money. Octane rating is purely a measure of a fuel's resistance to combustion due to compression.
What gas burns faster, 87 or 91?
And the 91 new ethanol fuel just made the fastest.
What will happen if you mix unleaded and premium gas?
Mixing two grades of gasoline will just average the two octane levels. For example, if you mix 89 and 91 octane fuel at about 50/50, the resulting fuel will have an octane of about 90. This means that even if you do accidentally mix octane levels, there's nothing to be worried about.
Will regular gas damage a premium engine?
Yes, using regular gas in a premium engine can cause damage over time due to engine knocking, which is a rattling sound caused by premature ignition. This can lead to performance issues like slower acceleration, reduced fuel efficiency, and may even void your car's warranty, as premium fuel is recommended for engines designed to operate under higher compression.
Potential negative effects
- Engine knocking: Premium engines have a higher compression ratio that requires fuel with a higher octane rating to prevent premature detonation (knocking).
- Performance reduction: The engine may not perform as efficiently, leading to a noticeable decrease in power, responsiveness, and fuel economy.
- Engine damage: While a single use might not cause immediate harm, prolonged use can lead to significant wear and tear on engine components from the knocking, potentially causing expensive damage over time.
- Voided warranty: Many manufacturers specify premium fuel in the owner's manual. Using the wrong fuel can lead to a voided warranty, which could be costly if repairs are needed.
What to do if you accidentally used regular gas
- Check your owner's manual: Confirm the recommended fuel type for your vehicle to understand the risks.
- Avoid hard acceleration: Drive gently, especially when climbing hills or accelerating, to minimize engine stress and knock.
- Add premium fuel: The next time you fill up, use premium gas to increase the octane rating in the tank. You can mix regular and premium fuel without issue, but you won't get the full benefit until the tank is mostly or entirely filled with premium.
- Consider an octane booster: If you need a quick solution, an octane booster can be added to the tank of regular gas to raise its octane level, but this is a temporary fix.
- Consult a mechanic: If you've been using regular gas for an extended period and hear knocking, have a mechanic inspect the vehicle to prevent further damage.
