Fuel Economy / Gas Mileage Sticky Index (look here for good info)

[cyclopathic]

question: do i still have to put a Fuel log even if i didnt had a full tank? or the Fuel log is only for full tank?

Not 100% sure how to interpret your question; do you mean you:
a) topped off tank and only put 2-3 gallons to fill it up?
b) or you added 2-3gal at expensive gas station just to get home?

if A) than you can enter data mi/km and litter/gal and reset trip meter.

If B) write down how much gas you put, do not reset trip meter and add liters/gallons you wrote down to total. So you may end up with something like 536mi, 11.7gal entry good luck