Non-alcohol gasoline = better FE.

[chuckm]

I typically take a 5% hit on my FE with ethanol. I suspect the 10% hit that some are taking is the result of ethanol's affinity for water. E-10 will actually pull moisture from the air, up to 0.5%.

[99LeCouch]

That could be. My car has an 18-gallon tank, and frequently runs for a week or two at a time with 10 or fewer gallons in the tank. So I can see how E10 drawing water into itself when it has a lot of surface area is doable.

But that begs the question of how the water gets in there in the first place. Possibly through leaky gaskets or when the evap canister draws in fresh air?

[gone-ot]

...from the EPA website:

GASOLINE lower heating value: 116,090 BTU/gal
ETHANOL lower heating value: 76,330 BTU/gal

...thus, ethanol has only 2/3's the ENERGY content of typical gasoline, although it does have a much higher OCTANE (anti-knock) value:

GASOLINE: RON = 88-98, MON = 80-88.
ETHANOL: RON = 116, MON = 112

...unfortunately, OCTANE is only useful to high-compression engines and supercharging, while ENERGY content is indicative of power and fuel economy. That's why E85 has a higher OCTANE value of 105, but actually results in 2-10% loss in power and fuel economy. If the engine had variable compression ratio (CR), most of the power loss could be reclaimed using E85 (which can use higher CR), but not the fuel economy.

...so, "yes," non-alcohol gasoline will yield better milage.

...FYI: GASOHOL is basically E15 (15% ethanol+85% gasoline).

[gascort]

My results agree - around 10% worse FE with 10% ethanol.

Bums me out because I used to be a huge supporter, thinking, "we could use 15% in every gallon we sold, displacing money we were spending on oil into money spent on corn, etc." But now I just wish they would put 100% gas in and charge me 10% more, or just put 10% less in my tank. Why make/use it - making it contributes to fossil fuel emissions, and on my car at least, doesn't even push it down the road.

I guess I do see one reason to use 10% - then they can sell 90% ~84 octane gas to you with the ethanol to boost octane to 87.

[99LeCouch]

^ That's another reason my car runs like poo on E10. The 3800 is designed for straight 87 octane, not 84 octane blended with ethanol to make 87 octane. My car is pre-ignition prone on low-quality 87 octane, so it pulls lots of timing to combat the pre-ignition. Every degree of timing it pulls is ~5 hp lost, so 8-10 degrees of timing pulled is 40-50 hp lost just above idle, when it pings the worst, and isn't making much power to begin with. So the computer dumps more fuel to compensate for the ping, and voila, worse fuel economy.

[tjts1]

The best part is that corn ethanol takes more energy to produce than it contains.

[Ryland]

I've noticed a 12-15% drop with E10, so have my parents who drive the same route every day and for a while made a note as to what kind of gas they put in, the pure gas tends to cost 3-5% more and you get better mileage... and use less gas then if they left left the alcohol out all together!
read up on alcohol engines some time, alcohol engines and gas engines are about as close as gas and diesel engines, sure I've mixed bio-diesel in with my gas and that worked but I'm not sure if it was really worth it, if I used less gas, but I was running a bio-fuel.

[PaleMelanesian]

The epa ratings for E85 and Gas on flex-fuel vehicles very closely match the theoretical loss due to the lower energy content of ethanol. Following that same math for E10, you get a 3% reduction.

Example: 2009 Ford Crown Vic
Gas: 16 city / 24 highway
E85: 12 city / 17 highway

GASOLINE lower heating value: 116,090 BTU/gal
ETHANOL lower heating value: 76,330 BTU/gal
E85 = 82,294 BTU/gal
82,294 / 116,090 = 70.9%

16 mpg * 70.9% = 11.34 mpg
24 mpg * 70.9% = 17.0 mpg

[MadisonMPG]

Originally Posted by 99LeCouch

^ That's another reason my car runs like poo on E10. The 3800 is designed for straight 87 octane, not 84 octane blended with ethanol to make 87 octane. My car is pre-ignition prone on low-quality 87 octane, so it pulls lots of timing to combat the pre-ignition. Every degree of timing it pulls is ~5 hp lost, so 8-10 degrees of timing pulled is 40-50 hp lost just above idle, when it pings the worst, and isn't making much power to begin with. So the computer dumps more fuel to compensate for the ping, and voila, worse fuel economy.

Do you have the same engine my dad does?

[99LeCouch]

If your dad has a 97 to about 2005 Impala, then I may have the same engine and transmission in a different chassis. 3800 Series II engine and 4T65 transmission in my car. The Impalas were either the 3400 or the 3800. The 4T65 can bolt to either.

Check the engine. If your dad's car has a black plastic upper intake manifold, it's a 3800. If it's flat aluminum stamped with "3400", it's a 3400.

If your dad is managing about 26-27 mpg highway with a 3800-powered Impala, that's about what a W-body gets.