firstly,what is the weight of 60 litres of fuel? if i run my car on a quarter tank will this improve my mpg much if i don't change my driving patterns and stick to the same mileage each week? it must make some difference as i will be carrying less weight.
less that 60 KG depending on what fuel it is...diesel or unleaded. 1 litre of water has a 1KG of weight....petrol is less dense than water, which is why it floats on top of water.
fuel specific gravity @ 60 degrees F= ~ 737
water = 1000
so about 45 KG (vry rough calc)
So yes, all things being equal you would save fuel.
Anything that makes your car lighter will use less fuel. As far as the petrol tank is concerned the saving would be tiny - just a few pence. Perhaps you should get a smaller car.
so if i drive with about three and a half gallons in the tank this will reduce the weight by about 95 pounds or 6 stone 10 pounds. that's a reduction of a small person! got to try this out. thanks for the input
4.5 litres to the gallon, 60 litre tank, bought the car new sept.1st last year and kept all fuel receipts. checked amount of litres put in and mileage so far and worked out to be 28.4 on urban as i only drive locally