Since 1984 I have tested 6 different cars to find out which fuel gives me the best "Miles Per Dollar". In every case I got the best results with mid grade gas by an average of 5 mpg. That's equal to 50 extra miles with a 10 gallon fill-up. Not bad for an extra $0.10 per gallon.

My 2008 Civic Hybrid is still in break-in mode (4000 mi. @ 50 mpg) and have been using 87 octane from the start. This week I have added my first tank of mid grade gas and am averaging 59 mpg! I will have a good average mpg in a few weeks for this higher octane fuel.

Here is a link to an article I posted last year about my 1989 Civic:

Save Money With Mid-Grade Gas

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This forum demonstrates ongoing mpg results from several Hybrid drivers measuring regular 87 octane vs. mid grade 89 octane.

My final results are in Post #40 on page 4

 

Maybe in your area the 87 has 10% ethanol, and the midgrade is 100% gasoline. I think that could explain the increase in mileage since ethanol contains less energy. Otherwise, it doesn't make sense to me how 89 would yield better mileage than 87.

 

Maybe it's the weather.

 

Agreed. steve1mac, I think you should switch back to low-test for your next tank and see how the mileage looks. I think you will see similar results to mid grade, but I would be curious to see.

 

I really can't explain it for your previous cars but there are several factors that could be affecting your HCH. Primarily it is in it's break in period and this car has been known to have a dramatic jump in FE as it gets through this. Even tires are stickier when new and have less rolling resistance after break in. Drivers have a breaking period with hybrids also as the car basically retrains some of the way you drive. My first tank in a HCH was 42.7mpg.

Plus there are the other things people have mentioned, weather, E10, and reformulated fuel for colder climates. In Illinois stations are suppose to label ethanol content but some stations might be sneaking it in there. Weather is a huge factor for FE, both temperature and rain / snow. The Mean High temperature for the first two weeks in May, in Chicago, was 68°F and 74°F for the last two weeks. Six degrees warmer during the day can have a real affect on your mileage.

There are just so many variables to take into consideration that I would not trust it to a single tank of gas. Since you already have the mid-grade fuel in there go for at least 1-2 more tanks of it and then switch back to regular for 2-3 tanks. You should be well into summer by then and the regular gas should have the extra benefit of even warmer weather & break-in period for car & driver even further along. If you still see a drop back to your pre mid-grade fuel usage then I would start to believe that is actually the fuel.

Could be an interesting experiment!

 

Yes Hemisync, I agree, there are several factors in play. I am also aware that fuel additives vary throughout the seasons.

With all my previous cars the break in period would last up to 5000 miles. I plan to go through 3 tanks of mid grade and by July I'll return to regular gas for 3 more tanks before I pass judgment.

With 200 miles of commuting I am running steady at 59.5 mpg on mid grade.
Time will tell.

 

Kristian,
I think it's best to stay on one fuel for at least 3 tanks to get a good average. Wind, rain, temperature, air conditioning, short trips to the store can all spoil the results of a low mileage measurement.

 

Yeah, absolutely. Just so long as you make the switch back to regular in a period of similar weather, A/C usage, etc. to keep things as apples to apples as possible.

I'm intrigued by your results. I found that I got better mileage on 87 (our high altitude mid grade) than 85 in my Contour, but in the days of $1.50 gas it didn't pay for itself for $.10 extra per gallon. Now when regular is $4.00 and mid is $4.10, the equation could be a lot better . Conventional wisdom around here says that there is nothing to be gained by higher octane, but I would like to see that proven.

Edit: BTW, I have just under 15k miles now and I STILL feel like the car is breaking in based on my summer mileage this year vs. last year.

 

Sounds like a plan, please be sure to update this thread when you are done. I will give it a shot myself and let you know what occurs with my 2005 HCH.

 

July in Chicago with no A/C??