2008 Expedition Owner’s Guide:
“We do not recommend the use of gasolines labeled as “Regular” that are sold with octane ratings of 86 or lower in high altitude areas”.
Shell in Denver, Coldorado (5,200 feet above sea level)
Regular $3.00…(85 octane)
Midgrade $3.15…(87 octane)
Premium $3.35…(89 octane) or is it 91 octane?
Before, the difference between grades was usually 10¢.
Using 85 octane gasoline instead of 87 octane, is performance/fuel mileage sufficiently diminished that we should spend the extra 15 cents per gallon?
It seems that we do get better fuel mileage using 87 octane. The odometer readout got up to 21MPG.
But there are so many variables I cannot discern if it’s the octane rating making the diffference.
Gas price map: