I have been keeping track of ALL the fuel that has ever been put into my truck. The attached graph MPG is all based on hand calculations (OK, computer calcs, but not the overhead). The red line is the actual calculation, and the black line is a rolling 4 sample average (but still based on the hand calculated values). In summer of '06 I was averaging 21 mpg which I ws happy with - Not bad for a 4X4, '610' w/ 315s on it!

 

Interesting. How cold does it get in your area? Seems to be quite a dip in the winter months, could be winter blend fuel. Do you add any additives?

 

Yeah, I though that it was intersting. Wanted to put the info together because I was tired of "your basing it on a 'best tankful' or overhead", "I can get 99.9 mpg downhill", "did you correct for tire size" tyope of arguments. At best, the fill up error would be over fillup & their has been 2793 gallons thru the truck. Even if the fillup error would be 1 gallon, the overall lifetime calculation would be accurate within 0.02%.

Back to your questions, based on the graph, I think that the truck did not fully break in & get the bes milage until it hit 25K miles (Dec. 2005). Winter mpg is 18 to 19 based on 2nd half of '05 & winter so far in '06. Mid summer getting 21 to 22 mpg. It's not terribly cold where I'm at, but cold enough where fuel is fully winterized - I work in Pittsburgh & live in Northern VA. BTW, lifetime mpg is 19.1 & includes city, highway, & some towing. Usually on the highway I drive around 65 & rarely over 70. And yes, I really do drive for milage.