I want to recommend the "Scangauge II", a small add on device which displays various stats about your car, most importantly, mpg. It connects to the OBD2 port on all cars made after 1996. The real-time display of mpg is incredibly useful and it makes efficient driving into a fun game. It costs $160, but it's well worth it.
I used to drive like most young men and I thought pretending to be a race car driver was the only way to enjoy the driving experience. Now, I strive for the most fuel efficient way to get from A to B. I would guess that using the SG2 has given me an extra 5 mpg, and I've only had it 2 weeks, and my wife does most of the driving (I ride a bike to work).
I have used one for the last 6 months. I was getting 600 to 650 miles per tank. I now stay around +- 700 miles per tank! Also keeping up with the tire pressure is another key item. I thought about getthing the tire pressure valve stem sensors on the next set of tires with another gauge to monitor them but that is another story. Anyone have any info on that?
My only beef with SGII is you cannot trully reset it...specifically in the MPG calc, since it uses the "fill-ups" to calculate the MPG.
I am not sure how the programmer cannot read the ECU's Full Tank signal, which is used to indicate full tank on the electronic dash, or move the needle for analog.
I pretty much got tired of putting the fill-up volume after wifey took a 2000 mile trip and forgot to input the refills, so my SGII shows that my tank reading needs to be readjusted down like 500% to finally correct itself.
If someone know how to do a hard-reset of SGII please let me know.
Check the manual as there is a reset somewhere in there. I had to do it just after i had it as I messed up and wanted to clear it all out.
If you miss a fill up like your wife did you don't have to readjust it if it was close the last time, just refill and wait till the following tank to adjust if needed. I have heard people only adjusting it half of what it says untill they don't have too. I went for a few tanks with it right on the money but then I guess something changed and I had to adjust it a few more times the last few tanks. Luckly I was getting better than expected mileage.