I would imagine that you're driving it, the only way to travel 400 miles and not have an empty tank is to always go down hill with the engine switched off :lol
Yeah I get about 400 miles to a tank if I behave, but at the current price of my WVO and RUG that I put in to keep things loose a tank is costing me £29
I never understand why people find it so hard to believe... It has been said on here so many times by people. Mine often does 420 miles on a tank, full to empty, as long as I do not boot it.