>>I get c. 100 miles out of the 1st 1/4 tank, so I think "Great, it looks like I'll get 400 miles out of this"
>>By 1/2 tank the trip odo reads c. 150 miles, so I think "Not so good, but it looks like I'll get 300 miles out of this"
>>by 3/4 tank gone it may be c. 210 miles, so I think "Well, I should get 280 miles"
>>
>>But the low gas bing-bing comes on at c. 237 - 247 miles and I usually have to refuel at c. 265 miles (this is mainly all urban - I get 300 miles on the motorway).
>>
>>Anyway, what gives? Does this mean it pays to keep your tank over 3/4 full all the time? I doubt it.
>
>
>But of course! You just did the math. An exhaustive, scientific, top-notch experiment. Of course, I would say instead that it is just the inaccuracy of the sensor and needle system, but that's just me. :-)

You should keep your tank partly filled so you don't waste fuel hauling around fuel.