Questins About Using E85 in a FVV

[Pontisteve]

Straight gas has a stoich of 14.64. E10 has a stoich of 14.08, and E85 has a stoich value of 9.85. 100% ethanol is 9.00. The difference between these numbers is directly related to the fuel consumption. So switching from straight gas to E10 yields a 4% loss in mileage.

Switching to E85 yields a 33% loss in mileage, but the fuel is cheaper. It's cheaper because Ethanol production is subsidized by our tree-hugging government. Which of course means we pay for it. So either way, we pay. And since E10 is still 90% gasoline, we're still buying 90% from the Arabs mostly.

E85 is 85% corn, which is sort of good, but that drives up the cost of food. And since corn is used in just about every food (corn syrup is a sugar replacement), the increase in use of corn as a fuel reduces the amount of corn grown for food purposes. Like all things with government, they try to fix one thing and end up breaking a few others.

If you have a flex fuel vehicle, you should run the tank close to empty before switching from one type of fuel to another. Then, once you switch, you should stay switched. In other words, pick a fuel and stick with it, for best mileage results. Otherwise, the O2s get to learn all over again, and mileage suffers while the car is "learning".

 

[Dalmus]

So now that I've gone back to straight E10, I'm now averaging 18.2mpg city, 19.8mpg highway. (I drive 15 miles on the freeway one way to work each day)

But, that only works with Citgo gas... So far, I've tried Speedway and Shell, and with those gasolines, under very similar driving conditions (3 hour trips to and from the cabin), I drop down to 16.6mpg city, 18mpg highway.

I didn't realize that different brands would make such a difference...

 

[Pontisteve]

If you really want to get crazy, check out this product:

http://www.zeitronix.com/Products/ECA/ECA.shtml

It uses a GM flex fuel (alcohol content) sensor to determine the % of alcohol in the gasoline you buy. It is placed inline in the fuel system, usually in the return line. Knowing that the stoich of gas goes down as alcohol content goes up, we then know that it takes more fuel per amount of air to get the same energy/power out of it.

So 14.7:1 Air/fuel for gas means 14.7 parts air, 1 part gas. The stoich of E85 is 9.85:1. That's 9.85 parts of air for every 1 part of gas. Since the air going into the engine remains constant, it's the fuel thats changing.

Using this alcohol content analyzer in your daily driver, you could find gas stations with the least amount of ethanol in their gas. And that would be the station that gives you the best fuel mileage.