Originally Posted by chestr

Here's my data for pretty much the life of my car, from mid-June 06 till now. Bottom tanks are the oldest. Started out with MFD showing upper 30s to 40 for my commutes, nominal tank FE upper 30s to a little over 40, but calculated out under 40 every time. Then winter hit, and MFD showed lowest tank at just over 30 mpg, during the coldest part of February, but calculated out under 30. Then come the 700 mile tanks, and solidly 40+ mpg FEs, for this summer (after learning more about the car's behavior, changing my commute to mostly off-highway, and some tips from here about going full-hybrid mode). And today's morning commute was showing maybe 38 when I stopped. Might have pushed it a bit higher for the last bit but not that much.