If you’ve ever stood at the gas pump staring at the options—87, 89, and 91 or higher—you might have wondered, Can I mix 87 and 89 gas? It’s a practical question, especially when you’re trying to stretch your budget without harming your vehicle. The short answer is yes, you can mix 87 and 89 octane gasoline, but the full story involves understanding octane ratings, engine requirements, performance impacts, and potential cost savings—or risks—associated with blending fuel grades.
In this comprehensive guide, we’ll explore what octane ratings really mean, whether mixing petrol grades is safe or beneficial, and what effects it might have on vehicle performance over time. Whether you’re a daily commuter, a road trip planner, or someone trying to cut gas costs, this article will give you the knowledge to make informed decisions.
What Do Octane Ratings Mean?
Before answering whether mixing 87 and 89 gas is safe, we need to understand octane ratings and their role in internal combustion engines.
Definition of Octane Rating
Octane rating is a measure of a fuel’s ability to resist engine knock—an audible pinging or rattling sound that occurs when fuel burns uncontrollably in the engine’s combustion chamber. The rating does not mean the fuel contains more energy; rather, it indicates how much compression the fuel can withstand before igniting.
Understanding Research Octane Number (RON) and Motor Octane Number (MON)
There are two primary octane testing methods: Research Octane Number (RON) and Motor Octane Number (MON). In the United States, the octane rating you see at the pump—like 87, 89, or 93—is the average of both, known as the Anti-Knock Index (AKI), calculated as:
(RON + MON) / 2
In contrast, Europe and other regions typically use RON ratings, which are generally 4–6 points higher than AKI ratings for the same fuel.
Typical Octane Levels and What They Mean
- 87 Octane: Regular unleaded gasoline, suitable for most standard vehicles.
- 89 Octane: Mid-grade gasoline, often used in vehicles with moderate compression engines or as an alternative when higher octane is recommended.
- 91–93+ Octane: Premium gasoline, required by some high-performance and turbocharged vehicles.
Most automakers specify the octane rating their vehicles require, and these recommendations are based on engine design, compression ratio, and other performance-related factors.
Is It Safe to Mix 87 and 89 Octane Gas?
The simple act of mixing different octane levels of gasoline—like combining 87 and 89—is perfectly safe from a mechanical and chemical standpoint. Gasoline batches naturally have slight variations in octane numbers, and gas stations blend fuels to ensure they meet minimum standards. Therefore, your car won’t be harmed if you mix 87 and 89 octane fuels.
What Happens When You Mix Gasoline Grades?
When you mix 87 and 89 octane gasoline, your tank ends up with a fuel that’s somewhere in between, roughly 88. This blended octane is unlikely to have any noticeable effect on your car unless it was specifically engineered to use only 89 octane or higher.
Chemical Compatibility of Gasoline Blends
Gasoline is fundamentally the same chemical product (hydrocarbons), regardless of octane level. Octane differences are achieved by blending with additives (such as ethanol or aromatic hydrocarbons) to enhance knock resistance. These additives are compatible and do not chemically react in ways that would harm your engine.
Can Mixing 87 and 89 Improve Performance or Save Money?
This question gets to the heart of why people consider mixing octane levels in the first place—either to enhance engine performance or reduce fuel costs.
Mixing for Engine Performance
If your car requires 89 octane and you sometimes use 87, mixing them occasionally may help reduce engine knock while staying within a budget. However, mixing a small amount of 89 into 87 won’t provide significant performance benefits unless the engine is specifically tuned to take advantage of the higher octane content.
Modern Engine Management Systems Can Adapt
Modern vehicles with knock sensors and dynamic timing control can adjust engine timing when inferior octane fuel is used. However, this adjustment often leads to reduced power and fuel efficiency as the engine compensates to prevent knocking.
Mixing to Save Money
From a cost-saving perspective, mixing 87 and 89 gas may provide marginal financial benefits. Gas price differences between octane levels vary depending on location and time of year, but the rule generally holds:
| Octane Level | Average Price Difference |
|---|---|
| 87 Octane | $3.00/gallon |
| 89 Octane | $3.15/gallon (plus $0.15) |
By splitting fuel fill-ups between both grades, you might achieve a middle-ground octane without frequently purchasing the higher-priced option.
What Vehicles Can Benefit from Mixing 87 and 89 Gas?
Not all vehicles are created equal when it comes to octane sensitivity. The potential benefits (or risks) of mixing fuel grades vary depending on your car’s engine design.
Recommended or Required: Understanding Your Owner’s Manual
Always consult your vehicle’s owner’s manual before making changes to your fuel type. Manufacturers often use phrases such as:
- “Recommended”—suggests optimal performance with higher octane but won’t damage the engine if used with lower octane.
- “Required”—indicates that failure to use the specified octane level may void warranties or cause mechanical harm.
High-Performance and Turbocharged Engines
For vehicles equipped with high-compression or turbocharged engines (such as BMW, Audi, or Subaru WRX models), premium fuel is typically required. Mixing 87 and 89 may not provide sufficient octane to prevent knocking in these vehicles over time.
Knock Sensor Limitations
While knock sensors help prevent serious damage, constantly using marginal octane can cause premature wear on engine components due to increased combustion chamber temperatures and erratic combustion.
Vehicles with Standard Compression Ratio Engines
For vehicles that operate at standard compression levels—like most Honda, Toyota, or Ford sedans—the risk of using a mixture of 87 and 89 octane is minimal. These vehicles are designed to run efficiently on 87 octane alone, and mixing in higher octane provides no real benefit.
Myths vs. Facts About Mixing Gas Grades
Despite what some myths suggest, mixing octane levels doesn’t produce a miracle performance boost or damage your engine in normal conditions. Let’s separate the myths from the realities.
Myth: Mixing 87 and 89 Gas Maximizes Fuel Efficiency
Fact: Fuel efficiency is primarily determined by engine design, driving habits, and maintenance, not small octane differences. Switching between fuel grades won’t significantly alter your fuel economy.
Myth: Always Use the Highest Octane for Better Long-Term Engine Protection
Fact: While higher octane fuels can help prevent knocking in high-performance engines, using them in engines designed for regular unleaded provides no real benefit. The knock sensor can typically manage lower octane fuel.
Myth: Mixing Gas Can Improve Cold Start Performance
Fact: Octane doesn’t significantly impact cold starts. Cold start behavior is more influenced by fuel volatility and engine calibration, not octane level.
When Mixing 87 and 89 Octane Fuel Might Be Beneficial
Despite limited overall performance gains, there are select situations where blending 87 and 89 octane fuel might offer practical advantages.
Territory Transitions Between Octane Availability
If you’re traveling in a region where 89 octane isn’t always available, having a mixed fuel strategy can ensure you maintain compliance with manufacturer recommendations.
Situational Engine Knocking
Some vehicles occasionally knock slightly even when using recommended octane, especially during acceleration or in warm weather. Blending with a higher octane fuel occasionally may reduce knocking incidents until you can pinpoint the root cause (carbon buildup, timing fault, etc.).
Fuel Dilution Due to Ethanol Variations
In areas where E10 (gasoline with 10% ethanol) is standard, octane levels can be marginally higher than the rating suggests due to ethanol’s anti-knock properties. Mixing 87 E10 and 89 E0 might result in octane blending that helps maintain the knock resistance needed for borderline models.
When Mixing Is Not Advised
While generally safe, there are situations where blending octane levels can lead to issues. Knowing when to avoid mixing ensures long-term vehicle reliability.
Vehicles with Direct Injection and High Compression
Modern direct-injection engines often run on tight tolerances and high compression. These vehicles may suffer from long-term performance degradation or increased emissions if the fuel octane is consistently below what’s recommended.
Using “Flex Fuel Blends” in Non-Flex Fuel Vehicles
Flex fuels, like E85, are high in ethanol content and require special engine components. Mixing gas with E85 can damage engines not designed for this fuel type and void warranties.
Trying to Mimic Premium Fuel
If your vehicle requires 91+ octane fuel and you’re attempting to substitute with a 87–89 blend, you are still risking engine knock and reduced efficiency. Blended octane won’t reach the required thresholds in many turbocharged, high-performance engines.
Gasoline Quality and Additives: What You Need to Know
Another important consideration is the role of fuel additives and gasoline quality. While octane plays a part in combustion resistance, the detergents and additives in different brands of gasoline can also impact engine health.
What Are Top-Tier Gasoline Brands?
Top-tier gasoline brands meet enhanced detergent additive standards beyond those required by the U.S. EPA. These fuels help keep fuel injectors, intake valves, and combustion chambers clean, potentially extending engine life and improving performance.
Examples of Top-Tier gas brands:
- Chevron with Techron
- Shell with V-Power
- Exxon with Synergy
- BP with Invigorate
What Mixing Does to Additive Concentrations
Blending different fuel grades can dilute or alter additive concentrations slightly, but no major issues have been reported. Using Top-Tier fuel regularly—whether 87, 89, or 91—can help counteract any potential variances in additive balance from mixed fills.
Final Thoughts: Should You Mix 87 and 89 Gas?
In the end, the answer depends on your car type, driving habits, and budget. Mixing these two octane levels is not harmful to your engine under normal operation and may be useful in a pinch or when trying to manage costs.
Key Takeaways:
- Mixing 87 and 89 octane gas is safe and won’t damage a standard vehicle engine.
- There’s typically no real performance gain from mixing the two octane levels if your car is designed to run on 87 octane.
- Turbocharged or high-performance engines that specify 89 octane should ideally use that fuel consistently.
- Always check your owner’s manual to determine required or recommended octane levels.
- Use high-quality, Top-Tier fuel when possible to support engine longevity and cleanliness.
If you’re looking for fuel cost optimization and own a vehicle that doesn’t strictly require premium or mid-grade fuel, mixing 87 and 89 can be a smart, safe short-term strategy. However, regular maintenance, including air filter changes, fuel injector cleaning, and proper oil service, will always play a more significant role in maintaining performance than octane blending.
Conclusion: Prioritize Your Vehicle’s Needs
Ultimately, while mixing 87 and 89 octane gas won’t harm your car’s engine, it’s also not a substitute for using the correct fuel type as specified by the manufacturer. Gasoline blends outside the recommended range, especially in high-performance vehicles, can lead to reduced fuel efficiency, unusual engine behavior, or long-term wear.
By understanding octane ratings, your vehicle’s engine requirements, and how fuel blending works, you’ll be better equipped to make decisions that are both economical and sustainable in the long run—without compromising performance or reliability.
Now that you know the ins and outs of mixing octane levels, the next time you’re at the gas pump, fill up with confidence, knowing you’ve made the right choice for your car and your wallet.