Winter Gas vs. Summer Gas

Slate has an article that explains this fairly well

http://www.slate.com/id/2098672/

 

i blogged this but the short answer is that it aint just the gas. in order of impact (my observation only here...2 and 3 can be swapped if on a longer trip)

1)summer formula gas freezes at very high temperatures (about 45º) so in winter, components are added to lower the freezing point and we are not talking about ethanol. ethanol lowers the polution levels but dont significantly change the freezing level. so the antifreeze components do take up space, but do not burn. depending on the area you are in, this alone will reduce your mileage 8-14%. a few select areas do not use winter formula.

2) your Prius is most efficient at a certain operating temperature. until it reaches that point, it will not get the optimum gas mileage. the colder it is, the longer it takes for your Prius to get there thus increasing the warmup time.

3) cold air is denser. that makes your Prius have to work harder to cut a path through the air. your oil is thicker which increases drag too.

4)Defrost...just as the air conditioning measurably lowers your mileage, defrost will too. according to CANVIEW, the defrost seems to use about triple the amount of power that heat does. unfortunately, for most of us, defrost is required. this year, i got one of those dessicant thingys you put in RV's and stuff to reduce moisture to see if it would lower my defroster needs. too early to report on that. i will say that last year, my rear window would get very wet (i rarely use the rear defroster) and i would have to take a towel and wipe it down about once a week or so. i live in Wa st on Puget Sound and the humidity is very high here.

but as i mentioned...it aint the gas. for me, look at my freeway average (i use this average because it is easier to control over longer periods and therefore results are easier to compare).

in summer at 60 mpg i averaged 59.5 mpg. no air. in winter, i average 49.5 mpg. because of the mildness of winter i have to believe that our gas is at the lower end of the spectrum or about 8% less. so about half is the gas, the other half is the 3 other items.