... Wait... beer? I've got a dyno shop out here in SoCal, but the beer may be a little warm by the time you get here.

Back on topic, though, I just went through my first tank of 91. My commute has stayed fairly consistent, and yet this tank I got my lowest calculated mileage: 35.21 mpg.

I'm planning on testing at least 4 tanks before I try to draw any conclusion, so let's help there's a huge jump in the next 3.

Oh, and yes, I did reset my ecu when I first filled with 91.

 

I'm not sure if anyone's still paying attention to this thread, but I'm gonna update it anyway.

I just went through my second tank of premium (91) and set my new record for lowest mileage. I averaged 34.43 mpg, significantly less than my last tank of 91 which got me 35.21 mpg.

For comparison, the lowest mileage I got with regular (87) was 35.34 mpg. I filled up another tank of 91, and I plan to fill-up with premium again when this tank is done. I'm hoping these next two tanks bump up the average.

 

I'm paying attention!

I think this is more an indication of a hot summer and running the A/C more. Or that extra trip to buy beer.

Premium fuel by itself should not decrease MPG significantly. Differences in stock blends and octane enhancers could reduce the energy content, but this change would probably be about the same as going between two different tanks of regular. I don't think it could be casually measured. It's just as likely to have slightly more energy content.

Thanks for the update.

 

Yeah, I think there are more factors affecting the change than just the octane. Although it has been unusually cool weather during the past tank, I have enjoyed a couple more pints than usual.

My thought is that even with other negative factors affecting the mileage, the use of premium would help at least keep the mileage equal to previous tanks. I was hoping for better mileage from the 91, so that even with the a/c on all the time, I would see similar mileage to 87 without a/c. That's why I wanted to test at least 4 tanks before looking for some pattern. It has heated up these past couple days, and it should be fairly warm into the weekend, so I wouldn't be surprised if this tank is low too. I'll keep my hopes up, though.

 

I think I'm required by the octane aficionados to ask if you have driven it "spiritedly" since filling with premium. The theory goes that it learns up to a higher spark advance.

Personally, this is counter-intuitive, at least where mpg goes.

 

For me, it's not that I drive it more spiritedly - the engine responds that way. This allows a more conservative throttle position, least that's been my experience. My last tank returned 37+ MPG 90%-highway driving. In my local world it's usually 39+.

 

I meant spiritedly as in:

Of course, if you drive with a heavy foot all the time your MPG is going to decrease.

 

I give it a few wot sprints after filling up. I do give it the occasional extra throttle when I'm feeling "sporty," but my driving style has remained fairly consistent from 87. My "testing" isn't the most scientific according to the numerous variables, but I'm more interested in real world results.

 

I haven't felt "sporty" since 1985.

Now "spirited" is a different story...

 

Time for another update:

I just went through my fourth tank of premium (91), and my average mileage with premium was 35.45 mpg. My average mileage with regular (87) was 35.67 mpg. The highest tank average with premium was 36.46 mpg, and with the tank of regular it was 36.02 mpg. All this was done over the course of June and July in Southern California, and my driving habits have remained somewhat consistent. With all the variables that could affect mileage, this basically leads me to believe that octane does not have any significant impact on the fuel mileage in my '10 GE. Considering that I also noticed no significant change in performance, and the fact that on average I spent 2 cents more per mile when running premium, it would seem that my GE won't be fed premium again any time soon.

 

I'm contemplating a dyno-and-beer night next week in Marietta. It'll probably end up like this:

Man Drives Home with Decapitated Body in Passenger Seat

Stay tuned.

 

Your results do not surprise me.. The state of California requires a multitude of additives to be added to all of the different grades of gasoline that would only be used in the higher grades in the other states.... Lower octane fuel has always resulted in better results at cruising speeds with a light load on the highway while higher octane works better in stop and go driving when you are having to accelerate frequently... I took it easy on my last tank that was driven about 60% on the highway at or slightly below the legal speed limit and lost 3MPG.... If I was driving a stock car that was driven gently at low RPM with a light load there would be nothing gained by spending the extra money on premium except for lower combustion chamber and exhaust temperatures but not enough to warrant the expense... My wife drives a Forester which has more drive train friction, rotating mas, wind resistance and weight than a Fit.. She beat me by one MPG on her last highway trip to San Antonio even with an hour long traffic jam from one side of Austin to the other.. She prefers to use premium fuel because she feels that her car has more power at lower revs and when passing slow moving trucks... 28.9 is pretty good for a car that size with AWD in 100 degree weather.

 

What additives are these?

I don't think this is true, but OK.



Goober's spreadsheet of stop and go driving over the course of a year doesn't support this.

Remember this kids: if you want to save fuel, drive fast and furious.

 

I haven't had my fit long (11 sport, AT) with 1,200 miles, but I have recently started trying to maximize my mpg. My driving is nearly 100% city driving, 2-7 miles per trip in a flat area. Light to moderate traffic and frequent lights/stop signs are the norm.

Being fairly light on the pedal, running 38psi in the tires, doing a bit of pulse and glide, and light timing has gotten me just over 30mpg (calculated) over 3 tanks of Shell 87 octane.

For the last two tanks I've used Shell 93 octane. The first gave me 30.8, the second 31.3 When I first switched to 93 I did the ecu reset.

In no way have I done a scientific comparison, but so far I'm less than impressed with the results, particularly given the roads driven, driving habits, and weather conditions have been consistent between the tanks and I use the same station for gas.

So, a couple of questions to those of you who know way more than I do about this stuff and have done much more testing...

Is there something I need to do (besides ecu reset) when changing octanes to get the most immediate adjustment to the change? <edit> I did do 3 short WOT's early in the first tank of 93 as well.</edit>

I'd like to give 93 a fair test, what else should I do or what should I change?

 

You're getting really good fuel mileage for a fit with an automatic transmission being driven in the city.. For best fuel mileage consistency I try to Fill up in the morning and fill to the top of the filler tube... A lot of people don't do it that way but I have for 5 years with this car without any of the horrible outcomes that have been said would happen... Other than lifting off of the throttle and coasting when I am going to have to come to a stop and accelerating to a higher speed when going down a hill or on flat ground before reaching a hill, and I also stay way back behind the car directly in front of me so I am not having to brake and accelerate constantly like most people are prone to doing... Generally I drive 80 or 85 MPH when it is safe to do so on highways... Your car is not even close to being broke in yet so your fuel mileage is bound to improve.

 

Its not what California adds but they take out. They use a RFG3 fuel which has less toluene and benzene. Its actually a good gas for power but not for mpg. Basically its alkylates and more ethanol. Toluene has more btus per gallon but weights 7.5 pounds and alkyates has more btus per pound but weights around 6.2 pounds. It also is based on the distillation curve. Premium has more middle Hydrocarbons but less end hydrocarbons. Regular has a Higher end HCs but not all the gas vaporizes. Ethanol has a higher temp and during start up most of it goes out the tail pipe as Ethanol which is clean lowering HC. When it vaporizes the added o2 requires more fuel. Toluene is great for higher intake temps because more of the fuel vaporizes causing the ecu to lean the fuel air mixture. Because its denser there is more energy available. Toluene works good with Ethanol or similar because the added HCs and the O2 kinda balance each other out with out adding more fuel and still lean it out.
The front end most of it is lost in the summer because at intake temps of 115, 5 percent is vaporized and dissipates before the spark is initiated.

Spark knock can happen even with premium if the distillation curve is not smooth. Knock sensor can fail and no code thrown. Most premiums has more upper lubricants. Not all premiums are the same, even from tank to tank from the same station.


This is California's RFG spread sheet, its close to what we have but we pay more for.

http://www-erd.llnl.gov/ethanol/proceed/rfg3.pdf

 

If what "we pay more for" is premium fuel, then your statement:implies premium fuel will not improve MPG.

In any case, the only standard for premium fuel in California and elsewhere is the anti-knock rating. Not energy content. Not detergents. Not lubricants.

 

<sarcastic snarkiness>Your car. To one whose manufacturer recommends or requires higher than 87 AKR fuel.</sarcastic snarkiness>

 

I pretty much drive the same way, other than also dropping into neutral if I get a chance to do the pulse/glide thing for a stretch. I'm stoked to get over epa rating and would be happy if this is all I get. Just looking to find the ceiling. I have heard it should improve a bit once I get some miles in.

To be honest, I may never see this high mpg again for this car since I'm moving and the new location has many more hills and way more traffic.

 

Yeah, yeah, I hear ya. No doubt, if my mpg doesn't improve soon on 93 I'll return to 87 and be satisfied that I tried it out and found it was not worth it for me. Of course, that's the whole point, to get direct experience before writing it off.