Gas mileage eastbound vs westbound

[EdwardC]

I went home to see my parents this weekend, driving my Element. I live in Chicago, but grew up in northeast Ohio, so I make this trip several times a year.

I use Fuelly to track my mileage and routinely find that I get significantly better gas mileage going east compared to coming back, going west. There have been times where I'll drive home, do an oil change, transmission fluid change and top off the tires expecting better gas mileage, then find out that I actually did worse.

I use cruise control almost exclusively (even though I know that it isn't the most fuel efficient method, especially on hilly terrain).

This past weekend, I measured 26.5 MPG heading east (engine warm, get gas, drive, pump again and calculate) then on the way back, I got 22.9 MPG. Carrying the exact same load. No work was done on the car while at home. I think I got my especially good gas mileage since it was cool enough on the drive out that I didn't need A/C. I used A/C about 75% of the time coming back.

Same trip back in May, 25.0 MPG eastward, 22.9 coming back. Most likely used equal amounts of A/C each way.

Some other things to note:

• Route taken: I-94 out of Chicago to I-80 the rest of the way
  
• Chicago Elevation: ~600ft
  
• NE Ohio Elevation: ~1,066ft
  
• Car downshifts up a grade about 4 times per trip eastbound
  
• Car downshifts up a grade 8-10 times per trip westbound
  
• My typical drive eastbound is at night, while my return is afternoon

These are the factors I can think of:

• Gas quality (eastern Indiana gas vs Ohio gas)
  
• Headwind vs Tailwind
  
• Something weird with the hills having less grade going east compared to west
  
• Ambient temp/Sun load on the car affecting the engine during the hot afternoon

I'm not too worried that there's anything wrong at all, just wanted to see if I'm missing anything.

Thanks for your thoughts!

 

[Quattro Pete]

I would guess headwind/tailwind. Most of the time the wind blows from west to east.

 

[Hokiefyd]

Wind direction plays an incredible role in fuel economy. Just a 10 mph breeze parallel with the road (at 70 mph road speed) means that you're aerodynamically driving 80 mph in one direction and 60 mph in the other.

 

[Drew99GT]

Most likely has to do with wind. In general upper air trade winds blow west to east in North America and there's less wind at night. Plus, if you ever do the drive after a cold front has come through, the wind will have more of a westerly component at the surface. Next time you make the drive, track the wind speed and direction. Look at flags, METARS weather data etc. to see what direction the wind component generally has. I always notice driving across Kansas (which I do frequently) better mileage going east vs going back west, but that usually occurs after a strong cold front has moved through since I'm coming back from storm chasing.

 

[BrianC]

Return during hotter temps is most likely the biggest factor. Cooler temps = better MPG. I live in FL. Pretty flat. Use AC all year. Fuel mileage is best in Dec., Jan., & Feb. Worst June, July, and Aug. Same roads, speeds and schedules.

Cooler temps=denser air= more efficent combustion.

IMHO

 

[Burt]

Has to do with the directional rotation of the earth and gravitational pull of the moon.

 

[ctrcbob]

1. I always get better from my Roswell location (heading east) going to Florida, vice when I go from Florida (heading west) to New Mexico. 1625 miles door to door. I like to say its because the wind is "normally" west to east, plus more down hill.

2. When I go to Western New York, I always get better mileage north of Virginia compared to south of Virginia. Much better mileage in Pennsylvania and New York. No idea why.

 

[EdwardC]

Interesting, I pulled some data from weatherspark.com for the approximate times I was driving through these cities:

Code:


Westbound:

City Time Wind Spd. Wind Dir. Temp

Hammond, IN 6pm 8.1 mph SW 72F

Elkhart, IN 8pm 6.9 mph SW 72F

Sandusky, OH 10pm 0 - 70F





Eastbound:

City Time Wind Spd. Wind Dir. Temp

Sandusky, OH 5pm 9.2 mph SW 82F

Elkhart, IN 3pm 8.1 mph W 83F

Hammond, IN 2pm 19.7 mph NW 80F


I'm inclined to agree that it's largely the wind. Clearly, the wind is almost always blowing from the West, and in some cases, very significantly. My Element is FAR from aerodynamic, so the 8 MPH tailwind much be helping a lot, and in some cases during windier weather, the eastbound headwind (almost 20MPH!) is really working the car harder.

According to my calculations, while cruising at 75 MPH, the force of drag with an 8 MPH tailwind is about 20% less, while the 20 MPH headwind increases for force of drag 60%. (I know that ignores that the direction isn't straight from the West, but it was just a rough estimate)

Sounds logical, thanks!

 

[hypervish]

I've noticed that as well, I make a trip to Michigan/Chicago a couple of times a year and always get better gas mileage heading back to NJ (east).

 

[MolaKule]

It was the Coriolis Effect!

 

[Vikas]

I learned quite a lot from this topic. Until today, I never realized that wind direction is reported as "from" direction. For some reason, I thought it would be "to" direction of the wind.

 

[EdwardC]

Originally Posted By: Vikas
I learned quite a lot from this topic. Until today, I never realized that wind direction is reported as "from" direction. For some reason, I thought it would be "to" direction of the wind.


I learned the EXACT same thing today. When I was on weatherspark.com, the only reason I figured it out is that they had a graphical arrow that roughly showed the direction, only then did I really put it together. I guess you never do stop learning...

 

[Hokiefyd]

Originally Posted By: EdwardC
I'm inclined to agree that it's largely the wind. Clearly, the wind is almost always blowing from the West, and in some cases, very significantly.


Yep. The wind wasn't always directly with you or directly against you, but it was always blowing in an easterly direction. This will certainly hurt your case, and that effect will be magnified by poor aerodynamics.

 

[Hokiefyd]

Originally Posted By: Vikas
I learned quite a lot from this topic. Until today, I never realized that wind direction is reported as "from" direction. For some reason, I thought it would be "to" direction of the wind.


We always look into the wind to see what's coming (in terms of weather). A NW wind means that we look to the NW to see what's in store (which is typically cooler and drier air). We look upwind to see "into the future", so that's why it's reported the way it is.

 

[Kuato]

Originally Posted By: EdwardC


[*]Car downshifts up a grade about 4 times per trip eastbound
[*]Car downshifts up a grade 8-10 times per trip westbound
[*]My typical drive eastbound is at night, while my return is afternoon
[*]Headwind vs Tailwind



You are right, and have answered your own question:
More downshifts with cruise = higher fuel usage.
Night = cooler air = more power/better mpg.
Weather in the US moves west to east = better mpg eastbound

I agree that the biggest factor is wind resistance. Oh, and the Hammond, IN wind did you wrong...

 

[thunderfog]

Originally Posted By: Kuato



Night = cooler air = more power/better mpg.


I'm not sure I like this part, although the temperatures we are talking about could make this correct at times.

 

[ironman_gq]

What are the elevations at each location? I regularly do about a 150mi round trip here. Starting elevation is ~1300' ending elevation is ~400' I always get better mileage going to this location on the first leg of the trip than I do on the return trip because it's all uphill. It might not seem like much but 900' of elevation change in an hours trip is enough to notice a difference in mileage for me.

 

[EdwardC]

Originally Posted By: Kuato
Originally Posted By: EdwardC


[*]Car downshifts up a grade about 4 times per trip eastbound
[*]Car downshifts up a grade 8-10 times per trip westbound
[*]My typical drive eastbound is at night, while my return is afternoon
[*]Headwind vs Tailwind



You are right, and have answered your own question:
More downshifts with cruise = higher fuel usage.
Night = cooler air = more power/better mpg.
Weather in the US moves west to east = better mpg eastbound

I agree that the biggest factor is wind resistance. Oh, and the Hammond, IN wind did you wrong...


Not sure which part you're talking about, but I did mess up the eastbound/west bound labels! oops.

 

[EdwardC]

Originally Posted By: ironman_gq
What are the elevations at each location? I regularly do about a 150mi round trip here. Starting elevation is ~1300' ending elevation is ~400' I always get better mileage going to this location on the first leg of the trip than I do on the return trip because it's all uphill. It might not seem like much but 900' of elevation change in an hours trip is enough to notice a difference in mileage for me.


I did note the net elevation change, weird thing is that it's actually uphill going east for me, a net change of about 500'.

 

[Sonic]

Funny, I have the same experience with my travels to my folks a few times a year. 300 miles one way and I use the exact same route on the way back home. Going there and driving northwest my MPG read out is always around 25.5. On the way back (resetting it) heading southeast I always end up at around 23.9. It's like this every time too! odd.