Yeah, some people probably get sick of reading about my MPG exploits. My wife says I’m an anorak, which I don’t think is a good thing. 
Took a long highway trip today, and managed 34.2 mpg round trip – 280 miles all told. The only difference I did between this and other road trips was that I stuck to 60mph (well, I hit 63 briefly going downhill once). Keeping that constant speed below the 65 or 70 on the various sections I was on gave me about a 10% boost above my extremely good records of 31-32 earlier. Driving slower really does boost MPG. That 10% is the equivalent of paying $3.50/gallon vs $3.85/gallon.
FYI, I’m driving a 2004 Chrysler Sebring (4 door, not the convertible) – Automatic, 4 cylinder. The federal data on the car (PDF) rates it as 21-28mpg. Driving more cautiously is getting me about a 20% fuel efficiency boost over the highest rating, and about a 30% increase over what my regular driving habits of a couple years ago were netting (23-25mpg on average, 26 in a pinch).
Try slowing down, just for a few days or even a week, and see what it does to your MPG and your wallet.
>> My wife says I’m an anorak, which I don’t think is a good thing.
Nope
Maybe it’s just a ‘guy’ thing.
I have a real-time mpg readout in my car – it’s very useful to get the instantaneous feedback. I hope it becomes standard in the near future, but I’ve also noticed it’s consistently about 2-3 mpg more optimistic than the ‘manual’ method (dividing miles actually driven by fuel actually added)
There are many factors that are thought to affect your mileage. Conservative driving is one, including gentle acceleration and braking (except where safety dictates otherwise of course)
Others that I’ve seen discussed are:
1) A headwind or tailwind (esp if you have a ‘draggy’ body style). IIRC: drag increases at the square of windspeed – double the windspeed and the drag quadruples.
2) Flat or hilly
3) The wear and inflation state of your tires
4) Other traffic
5) The fuel you put in the car
6) Your driving style that day
7) The weight of the car (were you carrying boxes of books some days?). Some people go to the extreme of half filling the tank twice as often, so they’re not carting around several hundred pounds of ‘unnecessary’ fuel !!!
I’m sure I’ve missed some as well
On #5: A while back I did a *long* road trip to IL – mostly flat, constant freeway driving. This took almost exactly 2 tankfuls in each direction, for which I was carefully (manually) measuring the mpg.
The first tankful on the return trip got significantly lower mpg (more than 5mpg less) than the other fills. After some head-scratching I realized the fill-up in suburban Chicago was 5% ethanol ‘winter formulation’
I only remembered halfway in to my long trip the other day that I did in fact have a big case of books and crap in the trunk. Not HUGE, but probably an extra 18-20 pounds of stuff I don’t need to be moving around. Now if I also lost another 20 pounds of my own flab, I’d get even BETTER mileage! Extra incentive to lose weight!
I’d do the ‘half tank’ thing regularly, but calculating my MPG would be harder and less accurate that way. I know the ‘pump shut off’ method on a filled tank isn’t 100% accurate either, but it’s a consistent method, and I generally use the same couple stations most of the time.
For the semester that just ended I commuted ~250 miles (round trip) once a week for a class. My 2000 Saturn got consistently around 35mpg at 80+/-5 mph for those trips. Above 80 acceleration is abysmal, and below 80 acceleration is less than ideal, but car gets great millage at high speed.
I think it all comes down to what your time is worth. Is a couple bucks of extra burnt gas a fair trade for an extra half hour of free or working time? I think so.
If mpg is the only metric of interest a 250cc Honda bike can get 60+mpg.
I’m finding that some of the ‘work’ I may need to do is stuff I can get done in the car with my hands-free ear thing and a cell phone. Therefore I don’t really see the tradeoff as completely black and white, but do get where you’re going with that idea.
I’m doing a mpg project too. I have an MG ZR 1.4 – 105.
The book says 41.3mpg combined, so far I have managed a 51mpg but that was a lot of night driving in the cold (heaters and lights on). I was coasting hills and keeping speed below 55mpg, slower if nobody is behind me.
I’m going to try another one soon when I am driving in the daylight only and go for 55-60mpg.
I’m hoping to pickup a C1 or Aygo 1.4d in the near future and go for 90-100mpg.