Best of times, Worst of times, how changing conditions can affect your fuel milage

[ChazInMT]

What a difference a day makes.

Drove from Chicago to Bozeman over the weekend, I stopped in Fargo for the night. Here's the contrast in Saturday and Sunday.

Saturday, stopped on my way in Hastings, MN to meet a friend, had time to kill since he wouldn't be done working till 6pm, so I took my time.

Temperature 60-65°F, 10-20 MPH tail wind, Avg speed, 55 MPH, took state highways for a fair portion of the journey instead of freeway so some hyper mileage techniques could be implemented.

Fill up MPG.....42.4 (513 miles on the Tank, a record best)

Sunday, it snowed during the night, I had 750 miles to go to be home, I did not care about fuel mileage that day. Screw Hypermiling...it's go time!

Temperature 12-20°F, 20-30 MPH headwind, Avg speed 75 MPH, Freeway cruise control set on 78 MPH.

Fill up MPG.... 27.2

Just another reason why anecdotal evidence of fuel savings is crap, same car, 2 days apart driven in 2 different manners and 2 different environments.

So you could view this as a 56% increase in fuel mileage or a 36% decrease, all due to how & when the car was operated.

[Diesel_Dave]

Excellent point. This is exactly why you need detailed records to verify improvements.

This is exactly why I keep weather data in my fuel log. See some recent analysis here:
http://ecomodder.com/forum/showthrea...log-23740.html

For my truck that 50 deg F temperature change alone would have resulted in a 25% decrease in mileage.

[slowmover]

Turning southbound into the daily wind does it here on the Coastal Bend. My new mirrors were vibrating ever so slightly. Until I realized that the combined wind speed against my road speed had me at 87-mph+/-. (I'll still re-tighten them and use some Loctite).