After convincing myself the 100% gas was better for fuel mileage, I seem to always get better mileage on the return trip.

I drive a lot at times, 300-400 miles each way, for business. I'd always start out with my 100% gas and return with (up to) 10% E. It seems I'd always put less in to top it off when I got home, than when I went out. I began to study this trend, whether at 55 mph or 75, the E gas would take me farther. Though at 75, the mpg were far less with either gas. I was able to study this trend heading out to the north or south, then east and west. No matter which direction, the return trip consumed less fuel.

This really confuses me... my son mentioned that maybe the engine is tuned for the 10% with it being a fuel injected engine, where maybe a normally aspirated engine benefits from the 100%. For 4 years, I've been paying $0.20 - $0.30 more per gallon feeling good about myself.

Can't find a reason to stay with the 100%. I have 232K on the odo.

Just thought I'd share...

 

Checked the difference in elevation between point A and point B? Maybe you are going uphill on the way out, downhill on the way back.

I always seem to get 1-2mpg better going from Atlanta to Orlando than I do on the return trip. Elevation, tail wind, etc... Not sure why but it is pretty consistent.

 

Ethanol has less btu's than the same amount of straight gasoline. No tune can compensate for that. You'd need to burn more to get the same amount of power.

 

Yep, elevation was my first thought too. Do you live in a valley or low lying area?

The digital display on my wifes Grand Cherokee can show MPG ranging from 6MPG going up hills (well, what we call hills here in Colorado) and it will fluctuate between 80MPG and maxing out at 99MPG on the down side of the drive for a good 20 mile stretch.

 

 

How much difference are we talking here. Are you always getting the 100% gas at the same station?

Newbie you cant really go by the instant mpg on the vehicle. It gives you a very rough estimate. Best way to calculate is by hand. The average mpg will give you a close reading when you reset it after filling up. I've gotten 24mpg out of our 04 grand cherokee with the 4.0. That was all highway at 65-70mph.

 

Yeah, but that's not really the point. The point is that it can take a significantly larger amount of gas to drive up hill vs driving downhill.

 

All the questions are obviously valid. I live on a pretty steep grade on Walden's Ridge (Signal Mountain), but I fill up (and refill) at the bottom so it takes that out of the equation. I also specify N, S, E and W as it should balance out any of the up hills and downhills.

I know this doesn't make any sense. Less BTU's, less efficiency, so lower mileage should be the result.

The best example that is con-fuddling: Driving to Greenwood MS, starting elevation is approx 656' above sea level (asl), ending elevation is approx 135 asl. I drive the exact route there as I do back, same speeds in every section, and I'd guess the elevation change takes place at the 75 mph section. It would be more efficient to run downhill (S) getting there, than the northern return uphill. I can get there on 1 tank + a few gallons to be safe. I top off before the return and make it home.

The North is tricky as there is a plateau to ascend pretty quick, but I always go down the back side before I return. The up is steeper than the other side, so I can see using less fuel coming home as the grade is different.

The difference is maybe 1-2 mpg, so that 10% is meaningful over 350 to 400 mile trip.

My latest trip to Greenville, SC, yielded about 17.5 mpg on 10% both ways. I was not able to get a difference heading there (or on the return) as my customer was off the beaten path 15-20 miles or so.

It's just odd..... but I guess I'm saving money now.

Food for thought...

 

Shoot.... all I know is, gas prices have spiked sharply with all this **** going on in Iraq. Ethanol or not, the Dakota is now parked and I'm driving my 4-banger Accord!

 

Report my post if needed, but ..................

To HELL with fightin' and diein' over oil for fuel/gas.
Put AMERICA back to work and turn coal into fuel/gas.

COAL LEGALIZE IT. COAL GASIFICATION