J7erry

I'm just wondering if there is a significant difference between running 91 octane "real" gas and 91 octane with ethanol added? We have a station that has no-ethanol 91 but it's 25 cents more a gallon and about 20 miles from my house? If it's no problem, I'd like to put the 91 with ethanol in and save 25 cents a gallon. Thought?

13V6coupe

Try both a couple tanks and see what your results are. But to state the obvious one has ethanol (ethanol bad) and one doesn't.

I typically run 93 ethanol free and get 2-3 mpg better mileage than running 91/92/93 that has ethanol.
Doing the math the 25 cent per gallon more for the ethanol free would be cheaper in the long run, I wish it was only a 25 cent per gallon difference here. the preffered station on my daily commute is 45 cents per gallon more for 93 ethanol free than the 89 ethanol fuel they sell at that station.

J7erry

We don't have anything higher than 91 here. I tried a full tank (14 gal) and didn't notice any mpg diff between it and 87 but the car did "feel" smoother to me.

potman

If I recall correctly, the owners manual advises against using ethanol. You might check and verify.

J7erry

It says not to use E-85, which is 15% gas. Missouri mandates the use, up to 10%, of ethanol in regular and mid grades. Most companies also put it in premium, but there are a few that don't. I was just wondering if 91 octane G-90 has the same effect as 91 octane G-100

WindyMustang

OK, so I'm going to take a stab at a moderately technical answer...but simplified a bit for easier thinkin'...let me know if anyone wants a more complete / complicated answer later...

OCTANE MEASUREMENTS primarily indicate how easily a fuel-air mixture will ignite. The higher the octane, the more easily it will ignite given a constant fuel-air ratio. The more easily it will ignite, the later in the combustion cycle one can set off the spark, and the more power we make (and the cleaner the combustion products by the way...so making power is good for the environment...really!).

So now I have 2 fuels that both have the same octane measurements, but one is 10% ethanol / 90% gasoline and the other is 100% gasoline. They will both support ignition under the same conditions, which is good!

Now for the bad news. The HEAT CONTENT of a fuel is dependent on the chemistry, not the octane. Since ethanol has a lower heat content per unit volume than gasoline, the more ethanol we add to the mix, the less heat we have to work with per gallon, so the more gallons we use to do the same work. As a result our MPG goes DOWN with ethanol blend, but the ignition properties remain the same.

Interestingly, E85 has a functional octane rating of ~95 (although some cite it as well over 105). It also burns at a lower temperature, or can be used to cool a hot intake charge. This can be GREAT for making power. However, E85 also has a much lower heat content than gasoline, so hopefully you won't have to go very far 'cause your MPG will drop for sure!

J7erry

Thanks Windy, that was great! I guess I'll stick with real gas. It also explains why the mileage went south when we put E-85 in my wife's flex fuel Taurus.

Nuke

Do your homework on what you'd save (or lose) by driving those 40 miles round trip (about 2 gallons) for non-ethanol fuel. I know that my mileage increases roughly 2 MPG with pure gas.

Oh, and there's an app for that, too. I had it on my android but dumped it since I have 2 or 3 no-ethanol locations near me that I use for the boat and yard equipment and, if convenient, for the Stangs.

vegas_

Good point about octane rating and energy in the fuel.
They are not related. And Higher octane does not mean better fuel.

Regular Gasoline has 114,000 BTU's per gallon (No Ethanol)
Ethanol has only 76,000 BTU's per gallon, that means much lower MPG

Ethanol is a very poor fuel, but the law mandates 10% in all gasoline
(It's a stupid political thing because Corn growing Iowa is the first presentational primary state)

AND Soon you will be offered E15 (15% Ethanol, with a 90 Octane)
Do not put this swill in any car, even though it will have an octane rating of 90
You will loose 2-3 MPG with this stuff, and possibly damage your car.

When you watch the news about the next Iowa primary, remember that whoever wins has sold his soul to the agricultural corporations in Iowa who grow corn.

The argument for Ethanol, is it's locally produced, not imported.
Which is true. BUT in a few years, most US gasoline will come from the US or Canada
because of the big new discoveries in North Dakota, Canada and Texas.

13V6coupe

Well I doubt that anytime soon, or even distant future will have the US using more of its own oil than import oil. US is too damn greedy and they will hord the **** until everyone else runs out before doing any serious oil mining on US soil.

But yes, ethanol is about big bucks, bribes and oh those poor poor farmers. It has nothing to do with the environment or polution.