OK, you're stupid (sorry. you KNEW I had to...)

That's my point... How can you call it "miles per tank" if you're not filling it up at the exact same point every time? I suppose you could figure a ballpark based on what's LEFT in the tank but it seems awfully inaccurate to me, especially when I can tell that something may be amiss when I see my monthly average drop, even if it's only 1/2 to 1 MPG. Whatever...

 

Haha, left ya open for that one

But I know in my diesel I always fill it til it tops off, then use that number and my miles. I wouldn't dare top off the stang though lol don't want gas running down her side.

 

Fair enough... Now that we jacked the OP's thread, too...

 

He hasn't been here in 10 posts and just a stupid thought, but to the OP have you thought about changing your fuel filter? Sometimes they can pick up a lot of trash and restrict the fuel flow. Who knows, I just always like to start with the stupid things (I.E. your tune like stated earlier) and work your way out

 

you're screwed man. nothing you can do about it other than drive like a grandma.

My job is 35 miles away, before I started car pooling i was getting 20mpg while doing 75-80 almost the entire time.

Now that I carpool, I drive to work myself once or twice a week. the carpool meeting spot is 3 miles from my house. So now my tank last over a week instead of 3-4 days, but now my gas mileage is ****ty due to the super short trips. its around 15-17 now, but that's only because I still drive the 35 mile trip sometimes. Without that highway mileage to bring up the average, I'd be down where you are easily.

Also, I changed my fuel filter at 30k, I'm at 36.5k now. I saw NO change what so ever.

Lastly, all my mpg is and calculated. The computer is way to optimistic. I've been logging fill ups here for over a year. Link

 

gas milage takes a ton of variables. you stated that you use to drive 75 to 80, was that highway milage at all or was it stop and go. You did state that your new route is stop and go and the mustang does use more gas and that is a fact for all cars. it is the reason that hybrids are better at stop and go then highway milage. during stop and go the battery is used more then the gas engine, (yes the engine doesn't move the wheels it charges the battery but at highway speeds the engine need to charge at all times). At highway speeds the 4.6l engine runs at around 32 to 35 mpg at constant speed and around town at stop and go 10 to 12 and when you add both together for a tank with both highway and stop and go you get on average 20 to 22 for a tank.
an engine also needs time to warm up, o2 sensors do warm up faster now around a minute to two due to the heated element in the sensor but the engine does need to time to warm up and until its warmed up you use more gas, so short trips use more gas then long trips. You also cause more sludge and damage to you car with short trips.

 

i always just go by the computer, even if it isn't dead on, it should be the same with respect to each tank as logging. like if i had a 2mpg drop between two tanks, the computer should pick that up just like logging would even if the number is inflated. btw, i'm almost 100% city so my average is like at 13.0mpg, so i need all of the inflated optimism the computer can throw at me to keep me from getting deperessed about using so much gas

 

Look on the bright side: Gas is more than 1/2 as much cheaper now as it was a few months ago.

 

Just a question, but can't you just divide the miles driven by how many gallons you put in.....assuming that you fill it up every time???

 

32-35mpg at a constant speed is only possible at 55mph. 60+ and its not possible unless you're going downhill. I've tested this before by setting cruise on the highway and hitting the mpg reset button. Never seen higher than 30mpg unless I was going downhill. Downhill I've seen as high as 50mpg, but that doesn't mean anything.

Also, those high mpg numbers only last for a few seconds. Give it 15 seconds or so and it goes down pretty rapidly.