[waynne]

I did an experiment over the last few months and have concluded that half tank fills mean the car will be more economical.

Dec (Full tanks) 2 fills = 35.6, & 34.9 mpg (£1.03 per litre!)
Jan (half tanks) 5 fills = 37.2, 37.2 37.3 37 & 36.9 mpg
Feb (full tanks) 2 fills = 35.9 & 36 mpg
Mar (half tanks 3 fills = 37.9, 37.2 & 37.3 mpg -Long motorway run for the first half tank (£1.10! per litre!)

Driving was very mixed over the months but I did seem to run a couple of MPG better. Any else tried this? In theory the less weight means you get better economy as you are lugging less weight around.

This is not scientific but I'd be interested to see your results.
I filled up from when the petrol light came on and filled with 23 litres of fuel each time for a half tank.