temp vs mpg
 

I have also been very interested in how outside temps affect mpg. I have been collecting data for quite a while, but honestly not sure how to compile it to make since.

Daily I kept track of my mpg, engine temp when done, adv speed, outside temp and if the engine was cold, warm (heated via coolant heater) or hot (as in just ran and is already warmed up.

If someone wants to take a shot with the excel data feel free.

It is at https://www.uwgb.edu/nevermab/mpg.xls

just to make sure your considering this... gas is formulated differently throughout the year depending mostly on weather.. which is a large portion of the reason why your seeing such a decrease in fuel economy in the winter.

Actually, many people overestimate the effects of seasonal gasoline formulations on fuel economy. In fact, most other factors affecting your cold weather fuel consumption play a much larger role than the reduced energy content in "winter gas".

EPA:
https://www.epa.gov/otaq/rfgecon.htm

I'm not sure our gas here in MN changes at all. We used to get ethanol added in winter only, as a oxygenate.(sp?) now we have e-10 year around. I can't tell any difference between summer and winter gas myself.

ELF -

I think that here in LA there is no reason for them to change the formula at all.

CarloSW2

We get the change up in NorCal. There is enough ethanol that you can actually smell it

I do understand that fuel changes as the temps change. I believe diesel has a wider total BTU change as the fuel changes for winter. I also run snows and often change their pressure between 30 psi and 45 psi depending on weather as well.

But what I am getting at is since I am on the same tank for about 4 weeks I can see a difference as the temps raises and drops, the fuel is the same the whole time so the temps has to be whats causing the change.