Using a higher octane gasoline than your owner’s manual recommends sounds like a good idea – after all, higher octane gas has higher performance and knock resistance for modern high compression engines. But is it actually better for your car, or could using the wrong octane gas potentially damage your engine?
Quick Summary
- Using a higher octane gas than recommended will not damage modern engines
- Higher octane gas does not increase horsepower, torque, or fuel economy in most vehicles
- The octane rating correlates to a fuel’s ability to resist engine knock – it is not a direct indicator of quality or energy content
- Only use higher octane gas if your owner’s manual specifically calls for it
What is Octane?
Octane is a measure of a gasoline’s ability to resist engine knock. Knock refers to abnormal combustion events that produce a metallic pinging or knocking noise from the engine.
Most modern vehicles with computer-controlled ignition systems are designed to operate on regular 87 octane gas. Higher compression performance engines may require premium 91-93 octane gas to prevent knocking.
Octane Rating Scale
Octane is measured on a scale from 0 to 100. Pure isooctane is given an arbitrary value of 100, while heptane is given a 0 octane rating. From these reference fuels, the octane rating of a gasoline blend is determined based on its knock resistance.
- 87 octane – Regular grade gasoline
- 89 octane – Midgrade gasoline
- 91-93 octane – Premium grade gasoline
Factors that Influence Knock
Several factors can contribute to engine knocking including:
- Compression ratio – Higher compression increases tendency to knock
- Engine load – Heavier load at low RPMs increases cylinder pressures
- Temperature – Knock more likely with hotter engine components
- Carbon deposits – Can cause hot spots in combustion chambers
Using a higher octane gasoline helps control knock by better resisting the extreme pressures and temperatures inside the engine’s cylinders.
Will Higher Octane Gas Improve Performance?
Gasoline with a higher octane rating than your owner’s manual specifies will not improve performance, horsepower, or fuel economy for most vehicles. Here’s why:
Horsepower & Torque
Despite popular belief, the octane rating does not correlate with the energy content or heating value of the gasoline. Instead, it relates to the fuel’s knock resistance. Since all grades of gasoline at a given station have very similar energy content, higher octane gas will not provide any more power in an engine calibrated for regular 87 octane.
Fuel Economy
Again, the octane rating does not change the fundamental energy content. Some premium fuels do contain more detergents and other additives. However, the impact of these on fuel economy will be marginal at best.
When Does Higher Octane Help?
The main benefit of higher octane gas comes from preventing knock in high performance engines. Examples include:
- Sports cars
- Muscle cars
- Luxury sedans
- High-compression turbocharged or supercharged engines
These engines produce more heat and pressure during combustion. Premium 91+ octane gas is required for proper operation without damaging knock events.
Will the Wrong Octane Damage My Engine?
Using gasoline with an octane rating lower than your owner’s manual recommends can absolutely cause engine damage over time. Premature engine wear comes from persistent knocking and uncontrolled detonation.
However, the inverse is not true – using premium gas in an engine designed for regular will not cause any issues. The higher octane provides added knock resistance, but modern engine computer systems will adjust timing as needed to match the fuel quality.
Potential Issues from Low Octane Gas
- Rough idle
- Loss of power
- Hesitation under acceleration
- Engine knocking or pinging
Continued operation with heavy knocks can damage pistons, rings, bearings, and cylinder head gaskets over time. But an occasional tank of regular gas in a car that requires premium will not cause noticeable issues.
No Problems from Higher Octane
Using a higher octane gasoline than the manual recommends will not cause any issues for your engine. The key reasons are:
- No change to fundamental energy content
- Computer systems adjust timing for actual fuel quality
- Added knock resistance is simply not utilized
The only potential downside is the extra cost of premium gasoline when regular would suffice in your vehicle.
Should I Use Higher Octane Gas?
Unless your owner’s manual specifically calls for premium gasoline, you generally should not use a higher octane fuel than the recommended 87 regular. Here are some guidelines:
Use 87 Octane if Recommended
This applies to the vast majority of modern cars. No performance, fuel economy, or other benefits will come from using 89 or 93 octane gas over regular 87. Follow the automaker’s fuel recommendation.
Use Premium Fuel if Recommended
Some high-performance vehicles with boosted, turbocharged, or high compression engines do require 91-93 octane. This helps avoid detonation issues. Stick to the recommended premium grade.
Higher Elevations
At high altitudes above 2000-3000 ft, the air is less dense and knock is more likely. Using 89 octane gas if 87 is recommended can help in higher elevation driving.
Older Vehicles
For older engines without knock sensors, it may help to run a grade or two higher than the manual states. This adds a safety buffer as the engine accumulates miles and carbon deposits.
In general, follow the automaker’s fuel recommendations for optimal operation. Going to a higher octane than necessary will not cause problems, but also provides no benefits in most modern vehicles.
Signs You Need Higher Octane Gas
If you start to experience unusual engine noises, vibrations, or loss of power, it could potentially indicate a need for higher octane gasoline in your vehicle. Here are some common symptoms:
Engine Knocking or Pinging
Persistent knocking or pinging noises from the engine are a sign of detonation. This indicates the fuel is not resisting knock properly. Switch to a higher octane gasoline.
Check Engine Light
Sensors that detect engine knock can trigger a check engine light. This is another telltale indicator that higher octane fuel is required.
Rough Idle
If your engine idles unevenly or rougher than normal, it could point to octane that is too low for your engine’s needs.
Loss of Power
Detonation can reduce maximum engine power. If you notice a lack of power under acceleration, low octane fuel could again be the culprit.
Hesitation Under Load
Difficulty accelerating and reduced responsiveness, especially under load, signals that higher octane gasoline is needed.
Switch to the next higher octane grade anytime your engine exhibits these behaviours after previously running normally on its recommended fuel. The extra knock resistance will restore proper performance.
Factors that Don’t Affect Octane Needs
Many drivers associate premium gasoline with improved efficiency and engine cleaning. But in fact, these other factors have no bearing on your vehicle’s octane requirement:
Additives
Detergent, injector cleaner, or other additive packages don’t change the fundamental octane rating or knock resistance.
Brand Name
At a given octane rating, Shell, BP, Exxon, and other major brands all produce very comparable gasoline.
Carbon Buildup
All gasoline can leave carbon deposits over time. Higher octane does not inherently decrease carbon buildup.
Engine Temperature
Running temperature may increase knock tendency but does not determine required fuel octane.
Focus solely on the octane rating rather than these other factors when choosing your gasoline. Use the minimum octane required by your vehicle for maximum efficiency.
How to Check Your Car’s Octane Requirement
Wondering exactly which octane rating your car needs? Here are the best ways to determine your vehicle’s recommended gasoline grade:
Check the Owner’s Manual
The easiest method is to consult your owner’s manual. This will state the automaker’s recommended octane rating for optimal performance and fuel economy.
Look in the Fuel Filler Area
Most vehicles have a sticker inside the fuel filler door or around the filler neck showing the proper gasoline octane. This should match what’s in your manual.
Contact the Dealer
If unsure, you can always contact your car dealer and provide the VIN. They will be able to look up the required fuel octane in their databases.
Try a Higher Octane
If you are experiencing knock or performance issues with the recommended octane grade, move up one level (e.g. from 87 to 89) to see if it helps resolve the problem.
Taking a quick look at your fuel filler sticker or handbook will reveal the right octane choice. Use the recommended rating for a good balance of engine protection and fuel efficiency.
Conclusion
While it may seem enticing to use premium 93 octane gas for extra power or performance, the truth is that it offers no benefit in a regular engine. The octane rating correlates to knock resistance, not energy content or added power. Using a higher octane than the manual states provides no advantages unless engine knock is occurring. It may cost a few more cents per gallon, but for most vehicles, sticking to the recommended 87 octane gasoline is perfectly fine and will not cause any engine damage.
