Hi,I have a nissan,put some fuel in,dashboard display said 99 miles left,hit the trip to see how it far was home,got home,said I had driven 1.9 miles,display said there was 92 left in tank!!,so 6 to 7 miles missing??

It works out your average MPG, therefore if you had been on the motorway, or driving economically before adding fuel it would show a higher range. Also starting the car uses more fuel, so sometimes if you had 100miles remaining arriving home one evening, the next morning it could show 80 as it has been cold started and used more fuel in the process.

Fuel also expands with heat, so there can be less volume of fuel when the car has been left overnight and its cold in the morning.

petrol thief??

Mine does that too, Maxandlucy but then on other occasions if I'm going at a consistent speed on the motorway for a long-ish distance, it will increase the number of miles allegedly left in the tank. It baffles me.

My Omega does exactly that. All that is happening is that
the "computer" assesses your driving and current consumption and recalculates the remaining miles you have left. So if you have a spell of heavy usage around town, the miles drop quickly but if you then get onto a motorway where consumption is less, your remaining miles will increase - seems wrong but is actually right. It is only a guide because it doesn't know if you might next have a spell of heavy consumption.

Same with mine. Low fuel light will come on and report 60 miles left on the info screen, but I can do ten miles at a steady 50 mph and the value won't change!

it's as StuyMac says, it works on averages.

i'll use the "bike" analogy:

petrol = energy

if you had say 100 units of energy in your body and it takes 10 units to cycle a mile then you can get 10 miles out of them 100 units. but if you had to cycle up hill you would use say 20 units of energy taking your expected distance for that amount of energy down to 5 miles, so if you're going faster/going uphill/driving into a strong headwind/in slow moving traffic you will naturally use more fuel than if you were on the straight and true's of a motorway cruising at a higher speed.

1 gallon of petrol in a car could get you on average 50 miles, so if you cruised down the motorway at say 70mpg's you'd do 70 miles, but if you were on side roads doing 40mpg then you would only get 40 miles.

it's all dependant on a number of factors.

All these theories flashed through my mind on one occasion when I noticed the petrol gauge falling over a five minute drive in a courtesy car I once had.

Unfortunately some toad had drilled a hole in the petrol tank to steal the fuel (Yes it WAS petrol too!) I had mixed feelings about the fact that he'd failed to blow himself and the car to bits in the process.

Rather less mixed when I realised the effect on my no claims bonus!