Too many variables, Sir, and meaningless to conjecture without more details about your unit. If your fuel economy deviates widely from mariner's (see post before yours), perhaps start with the simpler options first like tune-up. If you'll be having it done sa casa, their diagnostics might yield some clues. Assuming you conduct proper PMS on your unit and are judicious in your driving habits, the other major culprit might be the need for calibration of your diesel engine.

I, myself experience similar fuel economy as mariner. I get only around 8km/l in pure city driving, very short trips of less than 3km each direction around 3-5 days every week. But on highways, I do get 12km/l. No surprises there for me.

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