Hints to tweak a long-distance mpg test?

[doyourealize]

I just made a drive out from Texas to Georgia. Without a lot of notice (a family death) I didn't have time to make a clear plan for checking gas mileage, but I did do a pretty basic testing. I'm hoping someone here can offer suggestions for more accurate (and efficient) testing method on the way back (leaving tomorrow).

Basically, I filled up before I left, broke the trip down into various "legs" (not consistent with each other in time or length), and used the MFD's data (meaning I didn't fill up the tank & do the math to double check for "actual" vs. MFD). I didn't make notes on terrain (although there was a pretty even dispersal of hills, flats, etc. I think). The times I made notes on cruise control usage, there were always times when the cruise had to be disengaged for various traffic-related reasons for some periods. I didn't make notes or reset anything for bathroom stops, but I didn't ever leave the engine running, and I chose pretty easy ons/offs. These are the numbers I got:

Sherman, TX to Tyler, TX--160 miles--Cruise set at 65mph--A/C on Auto between 73-77--45.9 mpg

Tyler, TX to Shreveport, LA--90 miles--Cruise set at 73mph--A/C on Auto between 73-77--45.2 mpg

Shreveport, LA to Pearl, MS--217 miles--Cruise set at 73mph--A/C on Auto between 73-77--45.7 mpg

Pearl, MS to Meridian, MS--85 miles--Cruise set to 73mph--A/C on Auto between 73-77--46.1 mpg

Meridian, MS to Birmingham, AL--Cruise set to 70mph--A/C on Auto between 73-77--47.0 mpg

Birmingham, AL to Georgia state line--Cruise set to 65--A/C on Auto between 73-77--51.4 mpg

On the last leg, I did notice that the terrain seemed more universally flat, so that could have something to do with the better mpg.

Now, my differences in cruise control stem from a casual observation I made that, for 30 minutes or so on the same stretch of highway on a regular drive I make, there was no discernable difference in mpg at cruise on 65 and cruise on 73. For some reason, cruise on 70 seemed to be less than either. Any opinions on that?

I'd really like any and all suggestions to further tweak my test on the way home. Any takers?

Thanks in advance!

[JimN]

<div class='quotetop'>QUOTE(doyourealize @ Aug 18 2007, 11:45 AM) [snapback]498336[/snapback]</div>

I just made a drive out from Texas to Georgia. Without a lot of notice (a family death) I didn't have time to make a clear plan for checking gas mileage, but I did do a pretty basic testing. I'm hoping someone here can offer suggestions for more accurate (and efficient) testing method on the way back (leaving tomorrow).

Basically, I filled up before I left, broke the trip down into various "legs" (not consistent with each other in time or length), and used the MFD's data (meaning I didn't fill up the tank & do the math to double check for "actual" vs. MFD). I didn't make notes on terrain (although there was a pretty even dispersal of hills, flats, etc. I think). The times I made notes on cruise control usage, there were always times when the cruise had to be disengaged for various traffic-related reasons for some periods. I didn't make notes or reset anything for bathroom stops, but I didn't ever leave the engine running, and I chose pretty easy ons/offs. These are the numbers I got:

Sherman, TX to Tyler, TX--160 miles--Cruise set at 65mph--A/C on Auto between 73-77--45.9 mpg

Tyler, TX to Shreveport, LA--90 miles--Cruise set at 73mph--A/C on Auto between 73-77--45.2 mpg

Shreveport, LA to Pearl, MS--217 miles--Cruise set at 73mph--A/C on Auto between 73-77--45.7 mpg

Pearl, MS to Meridian, MS--85 miles--Cruise set to 73mph--A/C on Auto between 73-77--46.1 mpg

Meridian, MS to Birmingham, AL--Cruise set to 70mph--A/C on Auto between 73-77--47.0 mpg

Birmingham, AL to Georgia state line--Cruise set to 65--A/C on Auto between 73-77--51.4 mpg

On the last leg, I did notice that the terrain seemed more universally flat, so that could have something to do with the better mpg.

Now, my differences in cruise control stem from a casual observation I made that, for 30 minutes or so on the same stretch of highway on a regular drive I make, there was no discernable difference in mpg at cruise on 65 and cruise on 73. For some reason, cruise on 70 seemed to be less than either. Any opinions on that?

I'd really like any and all suggestions to further tweak my test on the way home. Any takers?

Thanks in advance!
[/b]

First, I am sorry for your loss. My stock suggestions are to increase your tp and block your grill. I am not convinced that the cruise control does a better job of maximizing fuel economy so I don't use it. Can you push the temp control up to 78 or 79?

[bwilson4web]

<div class='quotetop'>QUOTE(doyourealize @ Aug 18 2007, 10:45 AM) [snapback]498336[/snapback]</div>

. . .
These are the numbers I got:

Sherman, TX to Tyler, TX--160 miles--Cruise set at 65mph--A/C on Auto between 73-77--45.9 mpg

Tyler, TX to Shreveport, LA--90 miles--Cruise set at 73mph--A/C on Auto between 73-77--45.2 mpg

Shreveport, LA to Pearl, MS--217 miles--Cruise set at 73mph--A/C on Auto between 73-77--45.7 mpg

Pearl, MS to Meridian, MS--85 miles--Cruise set to 73mph--A/C on Auto between 73-77--46.1 mpg

Meridian, MS to Birmingham, AL--Cruise set to 70mph--A/C on Auto between 73-77--47.0 mpg

Birmingham, AL to Georgia state line--Cruise set to 65--A/C on Auto between 73-77--51.4 mpg
[/b]

I picked up my NHW11 03 Prius in Fort Worth and used I-20 to drive home to Huntsville via Birmingham. It was the first week of October and I didn't need to use AC. I broke the trip into 2 hour segments on cruise control and generated this chart:

I was lucky to not have any wind to worry about.

<div class='quotetop'>QUOTE(doyourealize @ Aug 18 2007, 10:45 AM) [snapback]498336[/snapback]</div>

. . .
I'd really like any and all suggestions to further tweak my test on the way home. Any takers?
[/b]

I'd like to suggest you treat this as your baseline. Then on the return trip, consider doing this:

1) Put the tires at maximum sidewall pressure (-2 psi on the rear tires) (record current values)
2) Check the oil level and bring it down to 3/4th of full (record current value)
3) Load the car, take an early nap and leave around 3:00 AM (you'll avoid AC for up to 6 hours and some wind)
4) Use 'air recirculate' with the AC (when you use it)

Map your speeds in 5 mph increments:
60 (if you feel comfortable with it or drive from Atlanta to the Alabama State Line)
65
70
75

Record the wind direction and speed. I typically use the flag method. Alternatively, remember the dates and time and you can look up the wind direction, speed and temperature from climate data of nearby towns going back a day or so.

On the return trip, starting early, you'll be able to compare and contrast travel with and without AC.

If you drive from Atlanta to the Alabama state line, it works best early in the morning when traffic is light. Hold the speed limit with cruise control and just drive. I was on that stretch three weeks ago and it is pretty ugly. I used the inside lane and made good time around midnight.

Try to use the slower speeds on the hilly segments since this avoids excursions into less efficient, high power modes.

I'm in Huntsville AL but I can take a short trip to Birmingham if the schedule works. Send me a PM and we'll see what can be done.

Bob Wilson