A few months back I persuaded my wife that it was good practice and worthwhile to fill the Nissan X-Trail with higher quality diesel, as although it was more expensive it would be better for the car and offer better mpg.

At the time Total were offering a money back offer that if mpg wasnt improved they would refund your money. Ever since we filled up with Total Excellium diesel and our mpg has dropped from 37 to 34.

We have filled up many times since then with different fuels but cant get the mpg back up to 37 even on a long run. All I can think is the fuel was a bit dirty and has left some deposits on the injectors or something reducing the overall economy?