On my van:
pressure to 50 psi=free
engine replacement=$500 (but it was that or buy another vehicle for more money; the old engine died)
partial grill block=$1 (had the vinyl siding lying around, paid a bit of money for the zip ties)
easing up on the gas pedal=priceless.
really, not much money in the van, the car is a bit different. And I don't put a lot of miles on the van either. But I've saved nearly $170 in gas over epa estimates anyways.
The Max
$50 for a used glass pack installed (mainly for acoustic benefit; it sound AWESOME now! But it also helps to hear the engine. When the rumbling reaches a cerain volume, it's about to downshift. And you can tell the gear by listening to the rpms vs the speed, so it's an eco mod
)
$130 scanguage. (THANK YOU EBAY!) it was practically new, and has taught so much about how to drive economically. Were it not for this site I wouldn't have ever bought it though.
50 psi in the tires=free
partial grill block=free
lower viscosity oil=basically free, had 10k miles on the old oil
learning how to drive a 200hp 4 door sports car economically=priceless
according to the fuel log I've saved $160 in gas in this rig, but she sometimes is driven with the spurs in her (ok, we love the acceleration and soundtrack the exhaust gives us a bit too much) so I think we're doing better. This tank we hope to get 30 mpg with a bunch of short trips, so that would be an accomplishment.