Dear SK.
I as i already told you most of my driving is intercity and i use to fill my car always neck to neck. Once i leave home (Lahore) use to take fuel from PSO Bhadru (M2 babu sabu) and and travel distance from bhadru is exactly 178km. And on return again take fuel from PSO (Kukrali Gujrat) and use to drile till my Home Back. (This is my travel cycle)
Now pFB in pic my Fuel log mentioning actual and display average

Above screenshot is showking difference between CITY DISPLAY & actual filling. And there is lite difference in both values which is less then 1 only. 201KM traveled in 10.81 litters. 19.0avg was on display and 18.59 avg actually calculated...
Now have a look at my recent travel log. 178km total driven and display is at 20.4 avg. And 2nd pic was taken after traveling 130km distance. Avg showing 21.5...

One more thing to add once again for all fellows, display of Avg on car is accurate but it always Hit due to "Haramzadgi" of fuel pumps. You can chk it by traveling 100KM with neck to neck filling and take fuel from different filling stations. You will get always different actual milage...
Now have a look at my travel summry calculated through navigation system. Attaching 2 different logs. One is rash driving (Brighter pic) and 2nd one is normal drive with max speed 90 approx... (More fuel efficient)
You will see that there is not much difference in travel time, only 15 to 20 minutes but huge difference in fuel consumption


The only formula to get extra efficency from you car is to drive at Max 80 of speed and have 20%-25% extra efficency with 5% extra time only... 


Have safe drive guys....
Thanks..
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