assuming you have a scangauge...
use trip mpg, reset the trip just as you enter your test section at the given speed. note your current trip mpg at the end of your test section. repeat the same section in the opposite direction and average the 2.
after all the runs at different speeds, i like to start over again to check data. my car seems to slightly increase mpg even after the thermostat has opened and will plateau after about 30mins of driving
and then theres also
http://ecomodder.com/forum/showthrea...ery-11445.html