What happens if you put 89 instead of 87?
In most cars designed to run on regular 87 octane, using 89 octane will not cause harm and will rarely yield a dramatic performance boost. The likely outcome is neutral or marginal, with any benefits more likely in engines prone to knocking or with higher compression. If your manual specifies 87, 89 is safe but not a guaranteed upgrade.
Understanding octane and why it matters
Octane is a fuel's resistance to knocking, which occurs when fuel detonates prematurely in the engine. Higher compression engines, turbochargers, and certain high-performance setups are more sensitive to knock. In the United States, 89 octane typically represents mid-grade gasoline and often includes up to a small amount of ethanol. Other regions use different scales (RON vs AKI), so the exact numbers can vary. Most modern cars have knock sensors that adjust timing to prevent damage, which influences how much benefit you might see from using higher-octane fuel.
When higher octane can matter
Higher octane can be advantageous in engines that have higher compression ratios, forced induction (turbocharged or supercharged), or a history of knocking under load or hot conditions. In these cases, 89 octane can help prevent knock and may allow the engine to run closer to its designed timing, potentially preserving performance and efficiency.
Before exploring specific scenarios, note that not all vehicles will notice a difference. For many everyday cars designed for 87 octane, the improvement from using 89 is often subtle at best and may disappear once driving conditions change.
- Better protection against engine knock in higher-compression or turbocharged engines
- Possible, but not guaranteed, improvements in throttle response or acceleration in some setups
- Generally higher cost per gallon with no guaranteed power or mpg gain for most drivers
- Increasing octane does not compensate for poor maintenance or incorrect air-fuel mixture
In summary, the practical impact depends on your engine design and driving conditions. If your vehicle is designed to run on regular 87 octane, you’re unlikely to see a meaningful difference simply by switching to 89, though it can help in specific circumstances.
Practical guidance for drivers
To decide whether to use 89 instead of 87, consider your car’s specifications, driving style, and cost. Here are factors that commonly influence the decision.
- Check the owner’s manual or fuel-cap label to confirm the recommended octane. If 87 is listed as the minimum, 89 is safe but not necessary for most days.
- Evaluate engine knock history. If you ever hear pinging or knocking under load, a higher-octane fuel may help reduce it or allow safer timing.
- Consider your driving conditions. Hot weather, steep hills, or frequent high-load driving can increase the likelihood of knock, where higher octane might help.
- Account for cost. Mid-grade fuel (often 89) is typically more expensive; weigh the potential benefits against the added expense.
- Be aware of ethanol content. Some 89 blends may contain more ethanol, which can slightly reduce mpg. In regions where 89 is paired with higher ethanol, the mpg impact may be more noticeable.
- For specialty or performance engines, or vehicles with a “premium fuel only” warning, follow the manual. Some engines are calibrated specifically for higher octane and will benefit more clearly from 89 or higher.
After reviewing these factors, many drivers find that sticking with the manufacturer’s recommended octane is the best balance of performance, efficiency, and cost. If you notice knocking or your engine’s performance seems off on 87, trying 89 once or twice (and monitoring for changes) can be a reasonable diagnostic step.
What about engines that truly require higher octane?
Some performance-oriented or high-compression engines explicitly require or strongly benefit from at least 89 octane, and sometimes higher (91–93). In these cases, using 87 can reduce performance, trigger knock, or cause the engine management system to pull timing, resulting in lower power or reduced efficiency. Always follow the vehicle’s fuel specification in these scenarios.
Note that even in those cases, the benefit of moving from 89 to a higher octane (like 91 or 93) is not universal and depends on the tune, age of the engine, and operating conditions. A modern car with a knock sensor may adjust timing to accommodate a range of octanes, but the largest gains typically come from using the octane that aligns with the engine’s design goals.
Summary
For most cars, using 89 octane instead of 87 is unlikely to produce a dramatic difference in performance or fuel economy, especially if the owner’s manual specifies 87 as the minimum. You may gain a small edge in engines that are prone to knocking or operate under high load, but you’ll pay more at the pump for a marginal or nonexistent gain in many everyday driving situations. Always prioritize the manufacturer’s recommended octane, be mindful of ethanol content, and consider your driving needs when choosing between 87 and 89.
Bottom line
The key takeaway is that octane matters most in engines designed to require higher resistance to knocking. If your vehicle calls for 87, 89 won’t hurt but isn’t a magic upgrade; if your engine benefits from higher octane, you’ll likely notice a difference in high-load or performance driving. For most drivers, the smart approach is to follow the manual and use the octane your car was built to use, while weighing the cost versus any marginal gains.
What happens if I use 89 in a car that needs premium?
Other things to consider: failing to use high-octane fuel in your premium vehicle could cause engine knock or pinging, which sounds like there's a large woodpecker under your hood; you could experience damage to your components; and using the wrong octant level could even void your warranty.
Does 89 burn slower than 87?
No, 89 octane fuel does not burn slower than 87 octane fuel; they both have similar burn rates. The difference in octane rating measures the fuel's resistance to knocking (premature detonation), not how fast it burns. Higher octane fuel is more stable and resists igniting from compression and heat, making it suitable for high-compression engines that require it.
Octane rating and combustion
- Anti-knock property: The octane rating is a measure of a fuel's ability to resist self-ignition when compressed. A higher octane number means the fuel can withstand more pressure and heat before detonating.
- Burn rate: All grades of gasoline have a similar combustion rate and energy (BTU) per gallon. While 89 octane fuel has a higher octane rating than 87, it doesn't have a different burn rate.
- Engine performance: You will not gain performance or fuel economy by using a higher octane fuel in an engine that is designed for 87 octane. The higher octane is only beneficial for engines that require it to prevent knocking.
- Engine requirements: It is best to use the octane level recommended by your car's manufacturer. Using a higher octane than recommended is a waste of money and provides no benefit.
Can I use 89 instead of 87 on Reddit?
It's almost always okay to switch to a higher octane fuel, it won't hurt anything. Putting a lower octane fuel than required is what can hurt an engine. Mixing different octane ratings is not going to cause an issue either, unless you're putting a lower octane fuel in than required.
Are 87 and 89 gas the same?
No, 87 and 89 octane gas are not the same; 89 is a higher-octane fuel that is more resistant to "knocking" or premature combustion than 87-octane gas. The numbers refer to the octane rating, which measures a fuel's ability to withstand pressure before igniting. While most cars can use 87-octane regular gas, some vehicles, particularly those with higher-compression engines, may recommend or require mid-grade 89-octane fuel.
- Octane rating: The octane number (87, 89, 91, etc.) indicates the fuel's resistance to pre-combustion, or "knocking," under pressure.
- 87 Octane: This is considered regular gasoline and is suitable for the majority of vehicles.
- 89 Octane: This is mid-grade gasoline, which offers more resistance to knocking and is recommended for certain engines designed for it.
- Engine requirements: Check your vehicle's owner's manual or the label inside the fuel filler door to see which octane rating is recommended. Using a lower octane than recommended can be harmful to the engine, while using a higher octane than needed won't provide performance benefits and will cost more.
