Not to hijack.. but you do know that tank capacity has nothing to do with calculating mpg right? I only as because lately I have found several people who had no clue...

 

Sure do, but if i would have filled up completly and not used the gas so much i could have gotten it to the mid 16

What i do is write down how much gas i put in, then when my gas light stays on (doesnt go on and off while driving down a straight road, etc.) i then take the miles and divide that by how much i previously put in.

 

Yeah, i guess it helps if you awake and paying attention.

Then 15 mpg isnt bad at all for a v8. i have always wanted the new 4R's with the v8 in it and S/C it. If you go that route let me know how the power is.

 

Nope, not the correct way...

Use what it takes to fill it up after you drive, or its not accurate.

look at this thread