Help - fuel nightmare!

[Youngest78]

Hi, I’m hoping someone might be able to help and advise. I have a 2009 Nissan Qashqai. It’s never been great for fuel economy, but the last few months it’s gotten unsustainable and something is clearly wrong; it’s not just simply ‘fuel-inefficient’. I don’t have a leak, garage has checked, but my petrol is just being guzzled almost instantaneously. It reads as an average of 25.7 MPG, which is bad enough, but it’s worse than that. I filled up from empty on Friday, abs my display read as per photo below. 338 miles. I’d say I’ve probably done about 50 miles max since then but after going down steadily during the wknd it now says I have 120 miles left. As I drive down a straight road the miles left come off in a matter of seconds. This is not because I only do short journeys (most of the time it’s the same domestic trips), or because I’m not filling up (as I just said, I do). Even at 25.7 MPG I would have gotten immensely more out of the tank full I just put in. I’m at my wit’s end, I don’t have the money to keep putting petrol in, but nobody seems to be able to suggest what the problem might be. 

[Trevor]

I wonder if the read out is faulty and the actual fuel is not dropping in the tank as it would seem

The best way is to fill to the brim, run the car for a while once the mileage is reset and then refill and calculate the mileage travelled and how many litres
Do a calculation and see what the actual miles per gallon work out at