I have Mira 2007, 4 Door Auto with Climate Control. I have tested fuel average 4 times so far and following are the results - Without AC & in City
1st Time: 19.25
2nd Time: 18.75
3rd Time: 18.60
4th Time: 18. 25
fuel average depands on following things,
a. quality of fuel used
In Japan fuel octane no is higher - milage calculated in Japan is based on higher fuel octane- results in better burning and lesser fuel consumption. In Pakistan fuel quality is very poor, I have tested PSO, Shell, Caltex, Total and found that each had different results with PSO as lowest followed by Shell, Total & Caltex. generally company operated pumps have better fuel.
b. Air Filtre Condition
engine burns fuel in presence of air, quality of air can improve or degrade you consumption. genearlly a dust free air filtre gives better milage. weekly air blow to air filtre will show improvement - specially if car is driven in dusty areas.
c. Lube Oil Grade
engine compartment wear and tear depends on quality of lube oil used, modren engines require higher specification lube oils. generally in pakistan we used shell/havoline etc which are non-synthetic or semi-synthetic lube oils invented for engines of 1980s-1990s. I have tested (Coure, Corolla, Alto, Cultus, Mira) with fully synthtic oil (ZIC A+ or same) and for all cars i found better results and improved milage. synthtic oil last for 7000 KM, cost per KM is lesser than traditional oil.
d. fuel injection system
fuel consumption will greatly change using electronic fuel injection while for manual pump fuel injection results will be poor. electronic fuel injection is closely associated with driving style.
e. Driving style
when you are stand still on a parking or on signal- due you push full throtle to accelerate or to be ahead of car standing in next lane, if this is your style than you would end up reaching fuel station earlier than that next lane guy. too much throttle will release extra fuel for compustion- extra fuel needs extra air and higher RPM to burn, higher RPM means more engine wear and greater consumption
f. Transmission system
everyone knows manual consumes less and auto consumes more, auto transmission cars with over drive gearing option will have lesser fuel consumption in auto (but still it will be higher than manual). reason is that over drive can reduce your engine power by shifting to next gear at a certain RPM which is generally lesser than 50% of total RPM car can afford. this results in less wear and hence better fuel.
I hope I have cleared.