What happens if you put 89 in a 87 car? (2024)

Putting a higher octane fuel like 89 octane in a car designed for 87 octane can have both positive and negative effects. The most notable differences come down to performance, fuel efficiency, and potential engine damage. Let’s explore this topic in more detail.

Quick Answers

Here are some quick answers to common questions about using 89 octane fuel in a 87 octane car:

• It may provide a slight boost in horsepower and performance due to the higher octane rating.
• There is little to no increase in fuel efficiency or gas mileage.
• It is unlikely to cause any short-term engine damage in most modern cars.
• Long-term use can potentially damage some older engines not designed for higher octane.
• It is considered safe in the short-term for most cars if 89 octane fuel is all that is available.

Octane Rating Differences

The octane rating is a measure of a fuel’s resistance to igniting before the spark from the spark plug. It is a measure of the fuel’s quality and higher octane fuels require more compression before igniting.

87 octane fuel is regular grade gasoline. 89 octane is a mid-grade fuel. The higher octane rating of 89 indicates it can withstand higher compression and temperatures without igniting early.

87 Octane

87 octane fuel has an antiknock index of 87. It is the minimum octane recommended for most regular cars on the road today. Using a lower octane than recommended can cause knocking, pinging or rattling engine sounds resulting from premature ignition.

89 Octane

89 octane fuel has an antiknock index of 89. The higher octane makes the fuel less likely to detonate early under compression, allowing it to resist knocks and pings better. This makes it better suited for high-performance engines with higher compression ratios.

Performance and Fuel Efficiency

One of the biggest questions with using a higher octane fuel than recommended is around performance and fuel efficiency. Will 89 octane give better gas mileage and horsepower compared to 87 octane in a regular car?

Horsepower

Higher octane fuels do provide a small boost in horsepower in higher compression engines they are designed for. However, in a regular engine designed for 87 octane, the gains are minimal at best. Some estimates are 1-3% power increase at most.

This is because the compression ratios are lower in regular 87 octane car engines. The higher octane does not significantly impact the ignition timing or efficiency of burning the fuel. So 89 octane will not provide a very noticeable horsepower boost in a regular 87 octane car.

Fuel Efficiency

Similarly, the minimal performance gains of higher octane fuel in a regular car do not translate into any meaningful fuel efficiency benefits. Estimates are a possible 1% increase in miles per gallon at most, often with no measurable increase.

In high-compression performance engines, the higher octane may provide fuel efficiency benefits by improving combustion efficiency. But in most regular 87 octane car engines, 89 octane does not offer fuel economy advantages.

Engine Load

One caveat is that running 89 octane may provide some additional headroom if you are often pushing the engine hard with heavy loads, like accelerating with a full load of passengers and cargo uphill. The higher octane provides a bit more knock resistance in highly loaded conditions.

Potential Engine Damage

One concern with using a higher octane fuel than recommended is the potential for engine damage over time. Let’s explore whether 89 octane can damage modern or older engines designed for 87 octane.

Modern Engines

In most modern car engines designed for 87 octane, running an occasional tank or short-term use of 89 octane is not typically problematic. The engine computer can adjust the ignition timing to account for the higher octane rating.

However, long-term use of 89 octane in a modern 87 octane car may cause issues in some cases:

• Oxygen sensors may get carbon buildup from running rich.
• Spark plugs may experience early fouling.
• Catalytic converters can get damaged from running rich.

To avoid potential issues, it’s best to run the recommended octane most of the time if the engine computer is tuned for it.

Older Engines

Older car engines from the 1970s-1990s did not have knock sensors or computer controls to adjust for different octane ratings. In those engines, long-term use of higher octane fuel than designed for can cause problems:

• Reduced lubrication inside the engine from less fuel evaporation.
• Engine deposits and clogged injectors from running rich.
• Sticking valves due to insufficient fuel evaporation.

Therefore, it’s not recommended to run higher octane fuels long-term in older engines without computer controls to compensate properly.

Usability in a Pinch

In a pinch where 89 octane is the only fuel available, it can be safely used in most 87 octane cars in the short term. One tank of higher octane is very unlikely to cause any engine damage in a modern car. However, it’s still best practice to fill up with the manufacturer recommended octane whenever possible.

Summary

Here is a summary of the key points on whether you can use 89 octane gas in a car designed for 87 octane:

• Minimal performance and efficiency gains, if any.
• No short-term damage but long-term use may cause issues.
• Higher likelihood of problems in older engines without knock sensors.
• Ok to use in a pinch if no other fuel available.
• Best to use manufacturer recommended octane whenever possible.

Always check your owner’s manual for the proper fuel grade for your vehicle. Going up or down more than one octane grade from the recommended level should be avoided when possible. Overall, the consensus is that 89 octane in a 87 octane car provides few benefits and some risks, so it’s ideal to use the recommended octane the majority of the time.

Example Scenario

Here is an example scenario to illustrate what can happen when putting 89 octane fuel in a car designed for 87 octane:

John has a 2012 Toyota Camry with a 4-cylinder engine designed to run on regular 87 octane gasoline. He is low on fuel and pulls into a gas station where the only options available are mid-grade 89 octane and premium 93 octane.

John decides to fill up with the 89 octane since it is closest to his car’s recommended 87 octane. After filling up, John notices a very slight improvement in acceleration but no noticeable difference in gas mileage. He continues using 89 octane in his Camry for the next 3 months to take advantage of the performance boost.

Over time, the engine starts to occasionally knock when accelerating. The performance gains are fading as well. In addition, his fuel economy seems to be getting worse. John takes his Camry in for servicing and is told carbon deposits have built up on his fuel injectors and oxygen sensors from running the richer fuel long-term.

The mechanic recommends John switch back to the manufacturer recommended 87 octane fuel and run some fuel injector cleaner through the next few tanks to clean out the carbon buildup. John realizes that while the occasional tank of 89 octane did not cause problems short-term, extended use resulted in issues due to the engine computer not being calibrated for the higher octane over the long run.

Conclusion

In summary, 89 octane gasoline can be used safely in 87 octane cars in a pinch, but provides few benefits. Long-term use of higher octane fuel than recommended can start to cause engine issues over time. To maximize performance and fuel economy while minimizing the risk of engine damage, it is best follow the manufacturer’s recommended octane rating whenever possible.