With fuel prices rising, do you need the more expensive grade of gasoline? If you drive a Forester, Outback, Crosstrek, Ascent, Impreza, or Legacy? Your vehicle is designed to run on 87 octane or regular gasoline, and you don't need expensive premium fuel.
Subaru's sports cars, the sport-tuned WRX, performance-tuned WRX STI, and BRZ rear-drive sports coupe, have a premium fuel requirement, but even with those models, check your manual for information on which fuels offer the best performance.
Gas stations in the U.S. typically offer three or more choices of fuel grades that vary by state, and Colorado provides an 85 octane gasoline. U.S. regulations require that each fuel grade be rated by its octane number and displayed on the pump. The most widely available fuel grades and their octanes, in general, are regular (87), mid-grade (89-90), premium (91-92), and in some states, super-premium (93-94).
Colorado provides 85 octane gasoline
A report from Subaru's Drive magazine says, "Every Subaru vehicle built in the past 30 years has relied on an increasingly sophisticated engine management system that constantly monitors the state of combustion inside the cylinders. Knock sensors relay information to the engine management system, and that powerful computer can automatically adjust the ignition timing to make the best use of the fuel in the tank."
In the report, John Gray, Field Quality Assurance Manager with Subaru of America's Service and Quality Department, says performance vehicles like the WRX, WRX STI, and BRZ are designed to run correctly even when the optimal grade of fuel isn't available.
The Owner's Manual states for WRX and BRZ models: "The engine is designed to operate using unleaded gasoline with an octane rating of 91 or higher." However, fuel with an octane rating of 87 or higher can be used in either model with no detriment to engine durability.
You may notice some small drop in performance using a lower octane fuel, but the vehicle will automatically adjust engine timing, avoiding a preignition condition.
Subaru says the higher performance Subaru WRX STI does require 93 octane gasoline for optimal performance. The Owner's Manual states that if 93 octane isn't available in your area, 91 octane is acceptable. The WRX, WRX STI, and BRZ also have decals inside the fuel lid defining the fuel requirements.
Why does Colorado offer 85 octane gasoline?
87 is the lowest octane rating in most U.S. states and is considered "regular" gasoline. In Colorado and surrounding states, including Utah and Wyoming, 85 octane gasoline is "regular," and 87 is considered "mid-grade."
A report from CPR News says, "The reason for this difference comes down to altitude, said Mahesh Albuquerque, director of Colorado's Division of Oil and Public Safety at the Department of Labor and Employment. Air is less dense at higher elevations, reducing the chance of engine knocking when using a lower-octane gas."
The report says a 2015 study from the Coordinating Research Council, a nonprofit supported by the petroleum and automotive industries, showed using 85 octane gasoline at 5,000 feet was more fuel-efficient than using 87 octane gasoline at sea level. "Arguably, fuel economy with 85 octane at elevation was better than 87 octane at sea level," Albuquerque said.
Except for the Subaru WRX, WRX STI, and BRZ sports cars, the Forester, Outback, Crosstrek, Ascent, Impreza, and Legacy models are designed to run on 87 octane. In the higher elevation states of Colorado, Wyoming, and Utah, you can buy 85 octane gasoline. Buying the regular 87 octane gasoline can save you hundreds of dollars per year in additional fuel costs.
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Denis Flierl has invested over 30 years in the automotive industry in a consulting role working with every major car brand. He is an accredited member of the Rocky Mountain Automotive Press. Check out Subaru Report where he covers all of the Japanese automaker's models. More stories can be found on the Torque News Subaru page. Follow Denis on Facebook, Twitter, and Instagram.
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