Let's use the ACTUAL facts, and not introduce gross errors by "rounding".

An average gallon of gasoline ( which varries from brand to brand and from geographic location to location ) has 115,000 btu of energy.

An average gallon of ethanol contains 76,000 btu of enegry.

Simple division reveals ethanol has 66% as much energy. Two / thirds as much as gasoline, not half.

Pure undenatured ethanol has a octane rating of 115.
Ethanol race fuel ( denatured ) has an octane of about 113.
85% ethanol, 15% gasoline, sold as "E85" has an octane of 105.

In most markets, the difference between "regular" gas and "premium or mid-grade" is the higher grades contain more ethanol. In many states, it is the regular gas that does not contain any ethanol, unless you live in an area that requires ethanol in all gas.

In the Mid-west, the "premium" gas with 89 to 91 octane usually costs less than the "regular" with 85 to 87 octane. This goes against everything we were used to in our childhood.

You should also know that more than 50 "blends" of gasoline are used in the U.S. alone. Making tracking MPG very difficult for the type of persons who track MPG to great detail. I travel for a living, and have given up on my minute study of mpg... which is pretty meaningless, unless you buy from the same pump day after day... but then that too will change with the seasons.

All that said, the highest MPG is always from pure gas.
10% ethanol reduces harmful emissions by 30%, while lowing MPG, in some cases, 10%, and in some other cars, only 3%. It depends on many factors.

However, I can get 30 MPG highway on E10. (10% ethanol)
I can get 29.5 MPG highway on E30 (30% ethanol)

So the drop in MPG does NOT follow a linear relationship with btu.
The drop from 10% ethanol is more than expected.
The drop from 30% ethanol is less than expected.

Hope that helps,
-John

 

P.S. to my prior post:

While MPG goes down with ethanol, HORSEPOWER goes up.

Many of my personal tests show that when I run more than 10% ethanol, my FEH will climb modest hills with cruise control ON, and the RPM of the engine hardly changes at all.

Last fall, I towed a 2,000 pound trailer one-way over the rockies (some 6% and 7% grades) burning roughly 30% ethanol and net 25 MPG at highway speeds. On the return trip, with the same trailer, I used E10, and got only 25.5 MPG, and the car had to rev to higher RPM on the hills.

 

If you're going to quote look at the whole issue:

"I don't think the E-10 is the culprit. Alcohol has roughly 60% of the energy of Gasoline. To figure the equivalency I just use 50%. So E-10 would have 95 % of the energy content of straight gas."

Too bad you're wrong.

Your whole discussion contains a little truth, as does all good sounding heresy, and a whole lot of shade tree mechanic stuff.

The energy content determines the Brake mean effective pressure coming out of the engine. That translates to horsepower to the rear wheels. From that comes the MPG.

Try again.

 

It's even worse than that. Gasoline is bought & sold as a commodity. There's no guarantee that the gas from the SAME station actually comes from a consistent refiner/brand from week to week. I drove past a Shell Oil refinery and was surprised to notice 5 trucks lined up waiting to take on fuel... 4 of which were for brands *other* than Shell.

Some of the more major brands might sell gas that only comes from their own refinery (although I don't know if that's even true) but the smaller stations buy gas from whoever has the best price from week to week.

Couple this with the fact that many states no longer require ethanol content to be labeled at all if it's less than a high percentage (e.g. 10% or less and they don't even have to tell you the ethanol is in the fuel) and it'll really drive you crazy. You'd have to do draw off a sample of fuel and test it each time you fill up just to know what you're *really* putting in your tank. <sigh>

I've also stopped trying to make sense of every tank's fuel economy. All I can do is monitor the things I can control (proper tire inflation, clean air filters, etc.), drive sensibly and try to plan routes on roads that "flow" well but don't necessarily force me to travel at 70 MPH freeway speeds -- but the mileage I get is the mileage I get because the fuel variation is something I just can't reasonable know or control.

...and I agree with Jason. Nothing will kill the fuel economy average of your tank more than taking many short (5-minute) trips on a cold engine.

I tend to get the best economy in spring and fall -- when temps are warm enough that I'm no longer starting on a freezing cold engine, but still cool enough that there's no need to run AC or drive with windows down.

 

Gasoline is a commodity... absolutely true. The majors make it and trade it between themselves and sell excess to the no-name companies...

The only thing you buy when you buy a name brand is their additive package. They trade the bulk gas back & forth when one is short and one has excess.

That is why over the years I have bought gas at the cheapest stations I could find. My Suburban has an Aux tank on it and when I fill it up it can take 67 gallons from bottom to top.

I can go nearly a thousand miles on a load of fuel so buying it at the least costly place makes a difference. Out here the difference between the east & west sides of the state can be 20¢ a gallon, so it pays

Regarding mileages I track each tank and have a spreadsheet calculate a mileage. So long as its about as expected, that's good enough. Highway= 15.x and town= 11 or 12. If otherwise then something needs to be looked at.

Frankly, I never saw a measurable loss of mileage with ethanol on the Suburban or Mustang.

 

Bill- Everything I posted is correct. I think you may have mis-interpreted things by reading them at 3:17am.

Adding ethanol to your tank will INCREASE horsepower if:

A) The quantity of fuel injected increases ( and it does )

and/or

B) More useful energy percentage wise is extracted from the fuel ( it is ).


The trick is tuning an engine to get more of B) with less of A).

Energy content alone does not determine MPG.
There's this little idea floating around called "efficiency".
The gas Escape and the Hybrid Escape both run on the same fuel.
How come one gets better MPG??? Hmmmmm.
Maybe you care to edit your earlier post regarding the "wrongness"?

 

If you don't understand the role compression ratio plays in B) above rather than tuning...

You'll never understand why you were wrong in you post.

 

It plays a HUGE role. One might even say, a primary role.
But not the only role.

I have detailed files and years of experimental data with gasoline and ethanol and blends of the two. My knowlege of ethanol is greater than most.
If you have any questions, I'd be happy to answer them for you.

Theory is just that, theory. And no, you ( nor I ) can change the laws of thermodynamics. No one is implying that.

What you don't understand are the complexities involved.
It is not as simple as you stated.
Some of the part you are missing is, the unexpected ways that ethanol plays with the car's sensors, changing engine parameters ( within its ability ) and sometimes, things don't fit your paradigm.

 

I never dreamed I'd get over 16mpg out of my '02 2WD V8 EB Explorer before owning my '05 FWD FEH. More than likely I drove like you back then and I would have never seen a measurable loss of mileage with E10 either. I expected 13.5 - 14.5mpg tanks and if I saw 11mpg I would think something was wrong with my Explorer. Today, I expect 21 - 23mpg from my Explorer with the A/C because I've learned how to drive wisely and take advantage of its design. For instance, I get better mileage at 42mph than I do at 35mph because the 4 speed auto will drop into 4th at 42mph. This drops RPM's and increases MPG so it's better to speed with traffic on 35mph speed limit roads and save gas.

When you maximize MPG on straight gas and then are forced to drive with only E10 you will see a measurable loss with E10. It may not be near as much as a I4 or V6, but it will be measurable.

The fact that ethanol is added differently in percentage with E10, it will keep the Long Term Fuel Maps in KAM all screwed up. This alone will constantly reduce MPG as the fuel maps are constantly changing.

GaryG

 

Gary and I can agree on this. E10 sucks!

I like ethanol in principle, but I hate the lack of regulation, standards, and poor marketing. I'm even finding many stations advertise pure gas ( regular "regular" ) and they too have ethanol in the tank. A rip off to the customer, since in the mid-west, E10 costs less than pure gas.

I say buy the chapest price stuff you can find.
By watching my LTFT closely, I know which stations are passing off E10 as plain gas.

Now... what to do... I want to "turn in" the station, but who's to blame?
And what's the "penalty"??? There's such little regulation, that it may not be any crime to pass of E10 as regular gas... in some states anyhow.

I want to promote ethanol. But I want ditributors / sellers to be fair about it.