(Not) Going the Extra Mile

[3050rpm]

Any suggestions as to what may be causing a sudden, small, but significant drop in fuel economy? I do a fair amount of steady highway driving, generally setting the cruise control between 70 and 75, and I had routinely been getting about 31+ mpg ('95 325i, 5-speed). Since November, however, over the same routes, I've only been getting ~29 mpg, a small but noticeable a 6-7% drop. The car has been running fine and smooth, the idle behaving as it should, tire inflation at 32 psi, oil changes at regular intervals, air and fuel filters replaced last spring. I've heard that colder weather adversely affects fuel economy (longer time to reach operating temp., denser air), but it really hasn't been all that bad where I live; also, winter formulations to make gasoline more volatile in winter can lead to decreased fuel economy, but I rather doubt all that much.

Again, this came about suddenly, which leads me to think that something mechanical went out of whack, as opposed to a gradual decrease over time. Possibly a vacuum leak? Thoughts, suggestions appreciated.

[gldfshkpr]

Do you buy gas from the same station? I've heard that during Winter months, stations are allowed to use more ethanol in the mix causing less M.P.G.

[3050rpm]

Ah-ha, yes I do, and coincidentally enough on those occasions where I have tanked up at other gas stations, they have the sticker saying "10% ethanol" on the pump, so thanks, mystery may be solved. Although that brings up a further point, we're paying quite high prices for gas as it is, and yet we're getting less for it, which means that gas (fuel) is on the order of 6% or so more costly than the posted price because it is 6% or so less efficient. Ugh.

[Exilion]

dont forget the 10% that isnt oil!!