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.
In general, no. Midgrade is for people who think a higher number on the gas pump = higher performance. It doesn’t. You buy the minimum octane that runs in your car without pinging.
That owner’s guide was written with lower altitudes in mind. You don’t need as high of an octane rating when you’re a mile above sea level.
“It seems that we do get better fuel mileage using 87 octane.”
To me that suggests that your engine is running less efficiently on 85 than on 87. More efficiency means not only better operation but also cleaner operation internally. Ergo, for your engine it’s a better fuel. To me that makes it worth the extra 15 cents.
I’m not willing to make that conclusion yet. In-car mpg guesstimators are notoriously inaccurate. Unless he does multiple tankfuls of each and records the miles driven and gallons filled for all of them, he can’t possibly know how much better or worse his mpg is.
You have to use what you have to use, regardless of the cost. Our Acura calls for mid grade and damage can result if not used regularly. My Pontiac can take anything so no problem. My small engines take premium. So gas for my snow blower is over $4 but for my Pontiac is around $3.
"...multiple tankfuls of each and records the miles driven and gallons filled..."
Emergent transports ruin such attempts. Burned half a tank of gas to a hospital where normally 1/3 tank is used.
Wish I had a real-time readout which compared fuel consumption to distance traveled.
Then I could also find the idea speed for return trips.
We have two cars with MPG computers. I consider them accurate to ±5% and an indicator of a general trends. I have not been able to detect any difference in gas mileage when using a higher octane gasoline.
I had hope that the knock sensor system would advance the timing as much as possible to take advantage of a higher octane but apparently it does not.
Ford recommends midgrade and you say you get better gas mileage with it. The cost difference is only 5% and you likely wouldn’t notice a change as small as 5% unless you measured gas usage accurately. It is at worst an even trade, so you might as well follow Ford’s recommendation.
I have used mid grade all my life, sure I know it is a waste of money, as my wife has always used regular, it is a philosophical thing, like building up idiosyncrasy credits, or brownie points with my vehicle. I can’t help it, OCD in a way, reinforced by life experience.
Maybe a month ago I was in another state and due to higher gas prices decided to put 10 gal of regular in. The car sat for two days (in temps around 0, not unusual since mid december), went to start it, and it failed. Sounded like it was trying to start on 1 cylinder. Starting fluid no help, jumper cables and heet, 45 min later started after trying every now and then. Coincidence for sure, superstition reinforced for sure. No codes stored or cel.
The sure indicator you need to upgrade octane is pinging.
Ethanol requires greater compression before it will ignite. That is why it is used to raise the octane of a gasoline. I guess you might say that it is harder to ignite because it requires higher compression.
Ethanol is added year round in many states because the corn lobby wants it that way. Ethanol is indeed a very unfortunate gasoline additive, no matter what time of year it’s added.
I’m not willing to make that conclusion yet. In-car mpg guesstimators are notoriously inaccurate. Unless he does multiple tankfuls of each and records the miles driven and gallons filled for all of them, he can’t possibly know how much better or worse his mpg is.
The computer most likely reads your instantaneous mpg just as accurately as your speedometer reads your instantaneous speed. The problem is, gas mileage averages exactly the same way speed averages. If you go 10 mph for one mile and 30 mph for the second mile, your average speed for that trip is not 20 mph, it’s only 15 mph.
Likewise, if you get 10 mpg for the first mile and 30 mpg for the second mile, your average mpg is not 20 mpg, it’s only 15 mpg.
Just for fun, estimate the average speed of you next road trip by reading the speedometer and then figure out the actual speed of that trip by dividing the distance traveled by the time it took. Most people are surprised that that trip where they went 70 mph most of the way only averaged 55 mph or so.