05 HCH, 19k miles currently. In case it matters my oil has been Mobil 1 0-20 since 10k miles, I just had a change at 16,000.
Well I've had 3, 600-mile tanks so I figured I'd take a leap and try for 700.
I filled the tank all the way to the very top (including the filler neck)...
It looked promising for the first 1/2 tank... 49.9 average MPG, then it rained for 8 days straight and the mileage average was only 43 (for those 8 days, I reset the 2nd tripometer to see if the rain effected it)... the last couple days was higher tho and I ended up with an average of 47.6 across the entire tank.
So guess where I ended up running out of gas?
(yes I had a small gas can with gas in it, intending on running it bone-dry).
698.9 miles!
SOOOO CLOSE!! It sputtered and died at 698.8 miles, I coasted to .9.
I put a splash of gas from the gas can into it, drove 1 mile to the nearest gas station and re-filled right up to the top of the filler neck.
14.60 gallons. which is 47.86mpg, which is about right since about 15 miles before it ran out, the ave. MPG moved up to 47.6. Take out the "splash" I put in there and it works out almost perfectly.
So... off I go again in my pursuit of the 700 mile tank.
I think it will happen this time.. warmer temps, probably less rain (it rained like 8 days in a row).
First 25 miles = 62mpg but given history I'm sure that won't be the norm.
That also, in case anyone wasn't sure... answers the question of how much gas is in a tank plus the filler neck... right durn close to 14.6 to 14.7 gallons.