I was getting 29-30 MPG all highway and cruised between 50-60 MPh

 

i get about 20-22 mpg and its 80% city driving (and i redline in first and second at least 3 times a day -- there are some open stretches in my commuting route for me to enjoy the hi-rev sounds ).

check your tire pressure, it does make up close to 10% difference in distance travelled (at least for me it did when i forgot to put air back in after a lapping day -- i was about 4 psi too low).

what i do for day to day commute is put in 1 to 2 psi above what's shown on the sticker on the door jamb helps a bit as well.

also do an oil change - who knows when the last time the previous owner has done so? afterall, if the oil is thick, your engine has to work harder (and burn more fuel) to keep up.

another thing i just thought of is you maybe in too low of a gear most of the time, i try to keep my revs between 2.5k and 4k rpm when coasting - so in city streets (60 km/h limit -- so that's what 40 mph for you guys?) i keep in 4th or 5th

 

i get less than 400 (KM) per tank.. do the math....

400 km / tank = BRUTAL (its actually 250 miles)

 

I drive 80 miles daily and I am getting 297 miles to tank so figure.

I think something is wrong with you air cleaner, injectors or something of that sort.

 

I average around 275 a tank (22-23 mpg) how the hell do you get 34 mpg in a S?

 

shit, i get the worst mileage in this case. average about 350KM on a full tank. I've tracked this for about 10 tanks.... anywhere between 325 and 365... and I consider my driving to be fairly mild....

spark plug inspection next perhaps... any other suggestions?

 

I average about 27-28 with city/hard/highway driving all mixed in. Normally get about 300 miles to the tank. I have a 07 btw.

 

Drive 65mph-70mph down the highway behind a truck. I got as much as 36mpg on my roadtrip to florida following a u-haul trailer.

 

its not an 06 thing" it must be a canadian thing!. .lol
..ya i plan on doing a tune up for sure

 

damn 18 is bad im supercharged and get between 27-30 and i do no highway driving to work at most 60 mph.