I did a 12 week experiment on mpg's using differant variables. in the 12 weeks i ran my tank till the light came on then filled up as soon as i could, which came to be 32 fill up's! i have a 24 gal tank and my light comes on when i have aprox used 18 gal. I drive 140-150 miles a day on the same roads every day to and from my shop. the weather conditions varied so i took the average on each test. all tests done w&w/o using the ac.

test1-stock tires on(265/70/16) normal driving:16.6mpg(been getting that for years)
test 2- code p0155 bad 02 sensor, normal driving:16.9mpg
test 3- new tires(265/75/16) cel on, normal driving:17.1mpg
test 4- same set up as 3 driving like grama: 17.6mpg
test 5- same setup as 4, but cranked the sound system as much as i could take it: 15.9mpg, these things are way to electically dependant!
test 6- the cel turned itself off, radio normal, driving almost like grama, using the cruise control alot, coasting to a stop as much as possible, just plain ole cruising and not in a hurry. averaged:17.9mpg had 6 tanks in the low 18mpg.
I will try to do this test come winter, i bet i wont break into the mid 16mpg range. sorry for the long read but i figured i would share my results on how much one little thing can change the gas milage and save money or at the same time COST you money!
P.S- I have a cap on my truck and i carry about 500lbs of tools as well. it is a 2001 AWD 4.7 QC with 193000 miles.

 

Did you calculate the numbers or use the ones off of the built in computer?

 

I find that interesting. Are you sure the radio wasn't making you work the bass pedal more than usual? (this sounds funny, but my friend actually does this sometimes without thinking, he'll start double bass'ing with the pedals)

Also, what gear ratio? 3.55 or 3.92?

On a related note, what bettery and alternator do you have? I think my window sheet said I have a 90 amp, I don't remmeber what battery. But I've only got a 70 watt sub amp driving a 8" sub, but wondering if I could factor that in. My city is almost to the teens, it's gotten slightly better with the OD off. Even my highway is starting to fade off. I changed the map sensor with the TB, debating doing plugs now. I also have the evap leak CEL on that i'm trying to trace a leak on.

 

i did the math myself, i dont have the built in milage thingy. i have a 136 amp alternator and a 750 amp battery(still the stock battery, holy crap, thanks for pointing this issue to me. 10.5 year old battery, wow) even with the cruize on i get crappy milage when crankin the stereo. i have a 1000 watt 12in sub powered by a 650 watt amp.

 

oh wow..thats a heck of a system, granted you have a quad. My sub is a 150 watt pioneer with a 70 watt visonik amp in a 1.5 cu ft enclosure, rattles my outside mirrors plenty. Would do more, but i dont have bassblockers on the speakers yet.

 

Did you do your calculations keeping in mind that your speedo is off because of the larger tires? Not a slam, just wanna know cuz I have that size tires and barely hit 16mpg

 

You'd get a more accurate reading of gas consumed if you: Filled up until the pump stops, drive most of the tank down, then fill it back up and compare your miles to how many gallons it takes to fill it back up.

 

this is my issue. I did my highway mileage using the actual distance traveled (per Google/"My Tracks" app) and also using the overhead computer. The computer was obviously short because it said i traveled 30 miles less than google said I did. So i calculated using the actual miles and got around 23 MPG. But city driving, I burn 1/8 of a tank every day, about 50 miles.

 

Um... turning up the volume shouldn't effect your gas milage. I think it is more like you can't hear the engine and aren't able to drive as effeciently.

Also, how fast are you usually driving on these roads? Is it mostly interstate? Or roads with a 50 mph speed limit, where you go 55. Thats where you usually get the best milage.

I think those numbers are pretty high for awd and a qc. Those are pretty close to the same numbers I see driving in 2wd with a manual... I can't believe you get around 18mpg with AWD and a QC, but I could be wrong. Also 193k miles doesn't help anything.

 

thats why i asked if he just was harder on the pedal because of the music. that said, amp-draw can affect mileage, it cayses the alternator to work harder.

Granted this is 100% unrelated, when our camaro didnt have an alternator, it actually was missing at the top end because the MSD didn't have enough energy to fire at 6500+RPM after the burnout, staging, and transbrake. The alternator was the only change, and it went away.

FYI, that's with 2 optima red tops in parralel. But a steer car is a completely different animal.