Why the Difference in Gas Mileage

[Bob Chadwick]

I just got back from South Miami. It's roughly 650 miles each way. On the trip down from Atlanta I got 26.8 mpg. On the way back I got 28.5. What's up with that. It was the same route and, if anything, we traveled faster on the way back.

I had the same experience with my Dodge Charger and my wife's Acura TSX.

 

[Tuna]

Tail wind or Georgia sucks. :L

Gas different? Did you bet 100% gas down in Florida? Did you use E10 for most of the drive down?

 

[Bob Chadwick]

Half tank of GA gas when I went down. Filled up in Florida once on the way. Half tank of Florida gas on the way back and a full tank of GA gas on the way back up. All gas a mix of 10% ethenol.

 

[BigJimZ16]

I just got back from South Miami. It's roughly 650 miles each way. On the trip down from Atlanta I got 26.8 mpg. On the way back I got 28.5. What's up with that. It was the same route and, if anything, we traveled faster on the way back.

I had the same experience with my Dodge Charger and my wife's Acura TSX.

Look at any map! It should be intuitively obvious to even the most casual observer... It's downhill from Atlanta to Miami!! You were going uphill all the way back!!! otfl

 

[Bob Chadwick]

Got to love a car that gets better gas mileage going uphill.

 

[BigJimZ16]

Got to love a car that gets better gas mileage going uphill.

Seriously, any difference in traffic patterns? weather, average speed, vehicle weight, etc.??

 

[Tuna]

Obviously, you released the parking brake for the return trip!

 

[Bob Chadwick]

Seriously, any difference in traffic patterns? weather, average speed, vehicle weight, etc.??

If anything we had a little more weight in the car coming back, the increase in elevation was coming back (Boynton Beach is at 30' while Atlanta is at 1,037') and I drove a little faster coming back.

It was cooler and raining when we were going down.

I see this everytime I make this trip and it doesn't seem to matter the car.

 

[Tuna]

It was cooler and raining when we were going down.

Rain and wet roads increases rolling resistance. Does it rain every time you head south?

 

[Bob Chadwick]

It does not.

 

[Huskerman]

I have noticed over the years on a variety of cars that the first tank on a road trip does not get as good as milage as the 2nd or 3rd......never been able to explain it.

 

[jmhorn52]

The wind can have an effect on gas mileage too

 

[tamashane]

I have had mechanics tell me that the computer will set a pattern to city driving as opposed to highway driving. Of course, in town you will not get as good milage due to the stopping and going. Once on the highway, you are pretty much going all the time and the computer resets itself to that condition, hence, better gas milage. I have noticed this in all my vehicles. If you want to improve your milage in town, take a short highway trip and reset that darn computer! I don't know if all this is true or not, but it does work that way. In my wifes Chrysler Aspen, after driving in town for awhile our milage sucks, but get it on the highway and it will go from 16 mpg to around 21 mpg. The tank on our way home always averages around 21 mpg from the start. Just my opinion.

 

[Hib Halverson]

We're talking 1.7 mpg which is 6% of the average...not a big difference. It's very difficult to measure fuel mileage accurately enough to make a comparison with that small difference. You have to drive exactly the same route at exactly the same speed, with exactly the same accelerations and decelerations, in exactly the same road/weather conditions on exactly the same fuel from the same fuel source.

That said, since the difference has occurred across different vehicles and difference instances of the trip, we can rule out differences in vehicles and weather.

What could make a difference?
1) A/C position inconsistent across all the trips, ie: not on going down and on coming back or on low going down and on high coming back.
2) Different kinds of elevation change, ie: 5 steep hills will use a lot more fuel then one long gentle incline.
3) Different driving conditions down and back, ie: you leave ATL at the same time each trip in rush hour traffic but you do not encounter traffic on the way back.
4) Fuel tank is not being filled in exactly the same manner with a difference on different directions of the trip, ie: one gas station you use going down is in an incline which keeps you from filling the tank full.
5) Window positions not consistent, ie: on the run down you have one window open but on the run back you have no windows open. Open windows can significantly affect aero.
....And so on and so forth

 

[Bob Chadwick]

Thanks for everyone's feedback. I don't think I'll ever know the answer. I just find it interesting that the difference is always better gas mileage coming back than going down.

 

[Huskerman]

I got to thinking....I'm always in a rush to get to the vacation spot and rarely in a rush to leave and get back home.......maybe that's why.....

 

[Bob Chadwick]

You are obviously not with your in-laws.:eyerole

 

[tamashane]

you are obviously not with your in-laws.:eyerole

lol!!!!

 

[Huskerman]

Har......10-4 on that......

 

[67vet]

You would think that the extra weight of carrying your in-laws back home would hurt gas mileage.