So ive been running 87 in my fit since I bought it 8 months ago. So this morning I filled my tank with 91 on accident. (Hit the wrong button.) From what I have read it doesn't make a difference in our cars but after approximately 100 miles can cruising around with the girlfriend I have gotten 6 or more mpg than I normally would have with just me in the car. Info coming from scangauge. I normally don't get more than about 24 mpg on my way to work. Today with full tank and the girl in the car I got 31 driving the same route. Is this something normal, my imagination, or something I should be concerned about. Maintenance for the last 10,000 miles is up to date and then some.

 

There are lots of different explanations for this difference. You did not state where you are located so I'm not sure what fuel you really were getting before or did get on this fill up. Also you did not state how much gas you put in on this fill-up so we do not know what the old / new mix was on this newest load of fuel. The energy content of 87 and 91 octane "pure" gasoline is very similar. In some areas of the country 87 is mixed with ethanol and this results in less BTUs (energy) per gallon. Also in some states an exception was made to allow 91 octane to be 100 % real fuel while 87 and 89 were require to contain 10% ethanol.

Another possibility is you are at the closing days of the winter mix fuel season. Winter mix fuel usually contains less energy per gallon due to a higher content of cheaper butane. After May 1st the EPA dictates the vapor pressure on all fuel sold at retail for on road use for all parts of the country. This means the refiners are now starting to supply summer mixed fuel which contains more energy per gallon in order to meet the May 1st deadline.

There are a few other factors like the engine the dynamic timing which is controlled by the Engine / Powertrain computer. There are modest gains that can be achieved by fiddling with these settings because most manufacturers set their tables on the conservative side. The prime concern of engine manufactures is meeting emissions standards. Next is making the engine last through the warranty period. After those were are met then we looked at MPG. As an example, the 14.7:1 air / fuel ratio that the industry settled on was not a number for fuel economy. It was a number for minimum emissions. We were able to easily run at 17:1 in lightly loaded engines which increased fuel economy (and emissions) considerably.

What you are describing here is a 30% increase in fuel economy. None of the above items should accomplish this. All I can say is be happy you have it better than before and if you can sustain these numbers, stick with the higher mpg fuel.

I could bore you with fuel tables, BTUs per gallon, and various ignition advance specs for various kinds of fuel at different rpms and engine loads. In the end, if you found something that works better, then go for it. If you stay with 91 this summer, you might want to go back and try a tank 87 in June or July just to see if it also has improved due to the summer EPA Vapor Pressure requirements. Around here 91 is only $.20 more per gallon. I know of one station where it is only $.12 per gallon difference. Fortunately we still have 100% real gas here and we consistently get in the 37 to 39 mpg range for mixed driving.

Good Luck

 

Thanks for taking the time to explain all of that. I think I will be just doing what you said about sticking with the higher octane fuel and enjoy it. I had no clue about the winter and summer fuel differences. I'm not too worried about it. thanks again.

 

Your daily commute is a different drive than a leisurely saturday cruise with the GF. Octane (the gas's) had nothing to do with it.

 

Glad you stumbled across it by accident. You see what Ive and others have been saying for years. Your engine is now more efficient and you can enjoy your better running car.

 

yessir. just fill it up with high octane and gain 30% MPG. I wonder why more haven't stumbled across this phenomenon?

 

You laugh Steve but I got 39 plus mpg all winter long.

 

Try more than one tank before making a decision to waste money. I tried 10 tanks, gas milage was actually less with premium.

 

I've averaged about 35 mpg for 25k+ on 87 octane. That's driving in metro Atlanta traffic. I agree with Steve. A daily commute and a leisurely drive will net very different results. When we went on a long trip with the Fit, no traffic, we got 41-42 mpg.

 

i am going to run this tank out then fill up again. so far mileage has been fantastic by comparison. if the numbers stay the same, it will not be anymore expensive to run premium and with how "happy" the car feels i think i will be sticking to it. thanks guys for your input.

 

Really?891

 

Really, Since I got this car in Sept. of last year I am getting 39.5 mpg average. A few tanks were lower but it still averages 39.5 calculated and expect mid to upper 40s this summer.

All on premium and Honda Bulk 0w20 semi synthetic oil.

 

I suggest that you try a few more tankfulls before you come to that conclusion. Once you have established the baseline for premium summer mix fuel where you are located, then go back and try 87 again. There is a good chance what you experienced is not sustainable for your normal driving patterns over a period of time.

If you will tell me where you are located, I'll call the company tomorrow and find out what the fuel requirements are for your area. I can find this out for most areas except Kalifornia.

 

I believe Steve was being sarcastic.

 

You misspelled "useless"

 

since i have switch from SHELL 87 to 91 GAS my MPG Are better, gas LAst long from what ive notice but who knows

 

I dont know if mileage will be better if one go from 87 to 90 or 91. Mileage can improve however if you switch from one brand to another. For example my old 04 CTS-V go 40 km per tank more on Shell consistently.

 

Realistically, there are a ton of variables to consider. That's why this "debate" is always in circles.

 

Careful, folks like n9cv will tell you you are full of it and insist its all the same for an area regardless of brand.

Mind you those of us who actually tune the cars know who's full of what, but that never stops the diehards.

 

well im just about halfway through this tank. according to the scangauge im getting anywhere from 4-8 mpg more than before per trip. i am planning on filling up again with the premium and actually calculating it out the "old school" way. since i didnt record anything on the last fillup. then i will try regular and compare the two and go from there. i did ask the attendant at the station if it was summer mix and he said it was. my numbers are still higher than i remember last summer so i guess i will just have to experiment and find out whats gonna be the best to use. thanks again for your guy's input.