Another thing that’s made financial sense for me is splash blending E85 with regular 87 gas.

My wife’s Acura MDX has a high compression J37 motor, and it requires a minimum 91 octane. The fuel tank holds 21 gallons total. I ran the math on this years ago, but I remember that if you fill up the tank with 1/3 of the tank being E85, and the remaining 2/3 of the tank with 87 octane Regular E10, it creates something like an ~E35 mixture that’s 93 octane equivalent. That’s 7 gallons of E85 and 14 gallons of Regular in the tank. I target a 93 octane mixture instead of the required 91 as a safety factor just in case the E85 is closer to the minimum 51% ethanol. Even with the approximately ~11% decrease in fuel mileage, splash blending her car with 1/3 E85 and 2/3 Regular comes out ahead $/mile wise.

The oxygen sensor in her car detects the slighter leaner fuel burn due to increased ethanol in the tank, so the ECU richens up the LTFT’s to compensate and get everything back to stoich.

 

I could be misremembering, but I’m pretty sure 33% is the hit taken on E85.

 

Since E85 can vary at the pump, it's more like 15-27% difference in mpg depending on alcohol content and driving conditions. So use 27% as a worst case.

 

I get about 10mpg on 85 no matter how I drive. On 93 I was seeing 12-14. This was just backroad driving and little freeway driving

 

Sounds about right.

 

Gas is almost $6 a gallon in my area. but E85 is around $3.49-$3.89 depending on the station....

 

Holy sheet…

 

In my 1500HD, I get 14 mpg on 93 and 10.5 on E85 when the ethanol content is in the high 70's to lower 80's consistently commuting back and forth to work. So it's a 25% hit in mpg. If E85 is 75% or less per gallon than 93, you are winning on cost. Stations here in MD charge 10-20 cents less than 87 for E85 and the difference between 87 and 93 seems to stay the same. They just all go up or down together. That means when fuel prices are high, 93 is the better deal. Often it's close enough that I still reach for the corn although during the price spike last month, I was filling up with 93. When I go into VA, E85 is significantly cheaper and it's a great deal. Traveling across the country, E85 prices are all over the place in relation to premium. The south and mid-west in general are great for E85 prices. The good thing about flex fuel, if you stop at a station or state where E85 is high, just put 91 or 93 in it.

 

On my way to work this morning.

 

That’s nuts…