MPG difference between 87 octane and 89 octane?

[herm]

I cant understand what is going on with these reports of big mpg losses... the energy difference is not that high, and the octane boost of E10 is not going to reduce the mileage.

There must be something else in the mixture besides ethanol that has changed... perhaps the timing on a Prius or FEH does not self adjust but I doubt it.

[08EscapeHybrid]

There's a noticeable difference in all of my vehicles, except my motorcycle. I haven't spotted a trend with ethanol free fuel in that vehicle, but then again, ethanol free premium is hard to come by, and I can rarely run it more than 1 tank. In my 98 GMC K1500, its a 2 MPG difference, fully loaded @ 70 MPH. In the FEH, I'll do 27-31 MPG on E10, and 30-36 MPG on ethanol free. My last tank in the FEH was 36.12 MPG (371.5 miles/10.284 gallons), and I had a fair amount of a/c use on that tank as well.

[RedylC94]

Originally Posted by herm

I cant understand what is going on with these reports of big mpg losses...

Maybe you're looking for an engineering explanation for a psychological phenomenon.

[some_other_dave]

In most stations, mid-grade is created by mixing the high-octane and regular-grade gas at the pump. The station only stores two grades of fuel, and they make the middle stuff by giving you a 50-50 mix of the two.

Some cars are set up to take advantage of higher-grade fuel than the minimum they require. Others are not. The specifics of the engine design and engine management system design generally determine that. However, there seem to be cases of individual cars reacting differently to changes in octane, even though they were the same model of car! So individual testing would be necessary to determine the effect in your case.

Ethanol has less energy content than gasoline. It's on the order of 30% less, which is one of the reasons that the "E10 Handicap" for our quarterly FE challenges is 3%. In theory, 10% ethanol will decrease your FE by about 3%. In practice, it is often different. Some cars appear to really be built for E0, and suffer a larger than 3% hit. Others don't seem to care one way or another. I wouldn't be surprised if there were a few that worked better with E10--but I wouldn't be surprised if there weren't, either. Again, testing of your particular car will help you determine how it reacts to fuel with ethanol in it.

-soD

[shadescape]

Originally Posted by some_other_dave

In most stations, mid-grade is created by mixing the high-octane and regular-grade gas at the pump. The station only stores two grades of fuel, and they make the middle stuff by giving you a 50-50 mix of the two.
-soD

can you provide any proof to this statement
I managed a gas station some years ago

[08EscapeHybrid]

I've worked in a couple of fuel stations, and newer "blender" pumps do that. Older stations with a separate tank for midgrade have it mixed when its loaded on the truck. Midgrade fuel is not refined, its mixed. The refineries only make regular and premium. Anything in the middle is a mix. When I worked for a Gov't run fuel station on a military base, when we ordered midgrade, the order was 1,000 gallons regular, and 200 gallons premium.

http://www.afdc.energy.gov/afdc/tech...etin_0210.html

What are blender pump dispensers?

Blender pumps are fuel dispensers that draw fuel from two separate storage tanks and can dispense preprogrammed blends of those two fuels. Many conventional stations today use blender pump dispensers to generate midgrade gasoline from a blend of regular gasoline and premium gasoline in their storage tanks.

[shadescape]

thanks for that info- never would have guessed

[EdwinTheMagnificent]

some other dave , I understand that your MINI asks for premium fuel. Have you tried different octanes ? What were your results ?

[some_other_dave]

Originally Posted by EdwinTheMagnificent

some other dave , I understand that your MINI asks for premium fuel. Have you tried different octanes ?

I have never used anything but CA-spec 91 octane premium fuel in my MINI. I will continue to use it as long as the car is under warranty, just in case.

The owner's manual says that 89 octane fuel is acceptable, but recommends that I use 91.

-soD

[chilimac02]

2-3mpg drop in my old accord from using e10. But now you cant buy e0 within 50mi of here.