why you guys always try to compare things at top level only. For comparing mileage all of following points should be considered:
1) Car engine type and power cc. Like in vitz we have 3 generations 1999-2004, 2005-2010, 2011+. Now if anyone in general says my vitz do this much then how would you compare it with yours. Also 3 cylinder engine would give better mileage than 4 cylinder.
2) Which mobil oil car uses. When I use 5W30 then I get around 30km's more as compare to when I use 20W50 which is not recommended for 1000 cc cars. Even Synthetic oil in same category as that normal oil also give 4-5% fuel efficiency.
3) Tyre size of car also have impact on fuel economy. I am using 185/65/13 i.e. wider tyre.
4) Which petrol do you use. I normally get 15-20 kms extra per tank when I use Total instead of PSO. However it doesn't mean that every PSO would be bad.
5) The daily traveling route also counts alot. As I normally get 9-10.5 km/litre with AC. But my route is 5.5km 4 times from home to office and back to home (22 km daily). This 5.5 km includes 3 signals and 6 speed breakers :-). On long route I get 520-550 from 40 litres tank.
6) Bad Wheel balancing and alignment can also cause you 5-10 % economy loss.
7) Manual Car would always give you better economy than automatic.
8) Bad fuel injectors can also effect fuel economy but in very very rare cases.
9) Driving style can also save around 5% fuel per tank.
10) Plugs can also cause bad mileage. They must be changed after 20-30 kms. If they have iridium tips then obviously they can last longer i.e. 70-80kms.
11) Most important of all MAF and O2 sensors. You can check them through OBD device.
12) Catalytic converter can also be cause for bad economy but in rare cases.
13) Bad fuel filter can cause you some problems as well but it normally starts with other indications like car loosing pick, start problem etc and people normally get to it early and change it. But according to my personal view it should be changed after every 3 years atleast.
14) Bad suspension can also cause fuel efficiency issues but in rare cases.
15) Low quality transmission/gear oil can also cause efficiency issues. transmission oil must be changed after 40k in automatic cars and whenever you do it the jali within gear box should also be cleaned.
16) Try to get your cars throttle body cleaned twice a year.
17) Many people calculate mileage in very wrong way. The right way is to get your cars tank to full level and wait for it to be empty and then calculate km/litre.
18) Loose or dead Timing/generator belt can also cause economy issues but to less extent only.
I hope these points would definitely help you.