85 octane? It's gonna ruin my engine. Chill, man. No, it's not.


May 17, 2000 (Updated Sep 19, 2000)




Here in Utah "regular" unleaded gasoline has an Octane rating of 85. Mid-grade is 87 and "premium" is 89/90, 91 if you are lucky.


85 Octane? But it will ruin my engine.

No it wont (probably). If your car is designed to use "regular" unleaded, 85 octane may be just fine. (How Octane can adversely affect your engine is discussed more in depth below.)

The reason the octane is lower in places like Utah and parts of Colorado is because they're at high altitudes, where the atmospheric pressure is lower. At lower pressure, you can get by with lower octane, which costs less and causes less pollution.

If you were going to STAY in that area for a while, you could use 85 octane, and your car would run fine. But if you're "on the road," and just passing through, use a mixture with some higher octane gas.


Can higher octane fuels give me more power?

If you are using fuel with the octane rating that the manufacturer recommends, the engine will already be operating at optimum settings, and a higher octane should have no effect on the management system. Your driveability and fuel economy will remain the same. Higher octane fuel costs more. Therefore, you'd pretty much be throwing money away.

However, if you have been using a fuel with a rating below what the manufacturer recommends, then using a higher octane fuel will cause the engine management system to move back to the original factory optimum settings, resulting in what might seem to be increased power and improved fuel economy.


Does low octane fuel increase engine wear?

If you are meeting the manufacturer's recommended grade of gas, you are fine regardless.

Engine wear is mostly related to design, manufacturing, maintenance and lubrication factors. The quality of gasoline, and the additive package used, would be more likely to affect the rate of engine wear, rather than the octane rating.

If you use a fuel with an octane rating below the requirement of the engine, the management system may move the engine settings into an area of less efficient combustion, resulting in reduced fuel economy and power.

Note: Do not use gas that produces sustained audible knock, or else engine damage will occur.


Conclusion

There is no advantage to using a higher octane gas than what the the vehicle's manufacturer recommends.

Use the octane that provides cost-effective fuel economy and performance. Anything more is waste of money and anything less could result in either 1) reduced power and reduced fuel economy or 2) an unscheduled, expensive visit to your mechanic due to damage created by engine knock.

However, you may want to compensate if the conditions change. For example, you might be able to reduce the octane of the fuel you use in winter and obtain the no loss of fuel economy nor power. But if it is hot and you are carrying a heavy load, you may want to use a higher grade.

Forget the stories about higher octanes having superior additive packages - they don't.


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