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Old 09-19-2012, 05:40 PM   #1881
bobdole888
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Member#: 316658
Join Date: Apr 2012
Vehicle:
2012 Impreza limited
5dr silver

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Quote:
Originally Posted by sgoldste01 View Post
I'm wondering if those of you who are able to achieve 40-something MPGs have found a source of gas that doesn't contain any ethanol?

All of the gas sources I've found so far contain 10% ethanol, and it's my understanding that ethanol contains less energy content than gasoline, so naturally my (and everyone's) MPGs suffer as a result.

(I'm sure the ethanol industry argues that the cost of my gas is also cheaper than gas without any ethanol, so I'm not at any disadvantage.)

The best MPGs I've gotten on a road trip is 37, so I'm curious if those of you getting 40+ are using gas without any ethanol.
First off, I'm not one of the guys getting 40+ mpg. However, I do feel that gas could have a lot to do with getting better mpg.
For the last 3 tanks of gas, I've been getting ~8% better mpg. This is without any change in driving pattern or weather changes. The only change that I can attribute it to is that my last 3 tanks of gas were regular 87 gas from Rotten Robbie. Previous to this, I was using regular 87 gas from either Unocal 76, or Valero.
The increase in mpg was instantaneous. The mpg meter started showing ~2mpg higher results soon after I got the Rotten Robbie gas.
At some point I'll fill up with Unocal 76 gas again to see if my mpg would drop when that happens. Then I would know for sure that it was the gas that made the difference.
Our impreza is equipped with knock sensor, so if it detects knock, it will automatically retard timing and make the engine less efficient --less mpg.
I'm wondering if the people getting 40+ mpg are putting in 89, 91 gas.
Or maybe they are in states which do not mandate ethanol in gas.
Here in California, ethanol blend is required by law.
For sure ethanol blended gas will result in lower mpg then pure gas.

For the record, my last tank of gas gave me 32.1 mpg(dash), 30.2(calculated). Less than 50% of my drive is freeway.
I'm slightly over the EPA estimate of 30mpg mixed.

I want to try 89, 91 gas at some point also to see if I get any boost in mpg from that.

The other point is tire pressure. I'm running 40 psi to help reduce rolling resistance. I've had problems with running manufacturer's recommended tire pressure in the past. They always seem too low and I end up with tires that wear out on the outer edges, but ok in the center. Hopefully running 40 psi tire pressure will result in more even wear and better mpg.
I've seen in Prius forums that people are running 50 psi over there and are not having any issues with tire wear. They claim to get 0.25mpg for every psi added.
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