Awesome mileage of 26 kmpl from my Swift VDi– using non-premium diesel

During my Jamshedpur – Kolkata - Delhi – Jamshedpur drive, I got a fuel efficiency of 21.2 kmpl overall (on a certain stretch I had measured 24 kmpl). So how come I got 26 kmpl overall (Jamshedpur to Bombay) now?

a) Engines (especially turbocharged & intercooled diesels) have much greater efficiency at low ambients. During this trip in winter the average ambient temperature was lower. I generally started every day at around 5 AM which gave me more time at lower temperatures.
b) The average speed during this trip was substantially lower (70-90 kmph as against 90-120 kmph during the Jamshedpur – Kolkata - Delhi – Jamshedpur drive. This probably is the most important contributor to the high fuel efficiency.
c) The use of AC was minimal (around 25%).
d) The fact the engine has now been properly run-in must have helped too.
e) My Jamshedpur – Kolkata - Delhi – Jamshedpur drive included quite a bit of city driving.

I must highlight the fact that an individual’s driving style greatly affects fuel consumption. Usually, I don’t accelerate or decelerate too rapidly, keep use of brakes to a minimum and try to drive at a steady speed on highways.

How do I calculate fuel consumption?

I take a lot of care in calculating fuel consumption because this is the single most important indicator of engine health. I note down the odometer reading whenever the fuel gauge needle is exactly aligned with the ½ tank mark. Next time the needle comes to the ½ mark, I again note the odometer reading and calculate the mileage by dividing the difference by the amount of fuel filled since the earlier reading.