Though it's an old post but want to share my experience.
I am getting 20-21 km/L avg on long in winter's whiles driving at constant speed of 100-110 max
In summers of 2022 I am getting 18-19 km/L with AC at Fan speed 1-2 and speed 100-110... Tyres are 155/80/13 and I keep pressure 36 all time.
Within city with AC I am getting 15-16 easily..
Some Tips to share from my personal experience!!
Tyre pressure should be kept 36 psi for WagonR as mentioned in door panel
Clean air filter after every 1000-1500 kms
Clean Air sensor and Map sensor in every tuning (after15_20k kms) you Can do it at home very easy.
Keep ac at fan speed 1 or 2.. it saves fuel.. rest you can adjust accordingly to your need . I always keep at 1 and I feel comfortable at this speed.
Drive with patience and Relaxing..don't rush..you don't need to rush, you are wasting fuel because of unnecessary speeding and braking.. accelerate slowly, I usually put 5th gear at 60 km/hr.. observe situation on road and traffic in front of you and adjust your speed by releasing your foot from pedal..not by agly Gari k sir py brake lgana.. apko samny u turn Lena hai to approach slowly by gradually decreasing your speed by lowering gear or by releasing your foot from race pedal.. gari u turn tak bhaga k ly k jaingy r phr brake lgaingy to apny wo Sara fuel waste kia..
Switch of your Engine at Signals..don't do unnecessary idling..
These figures are ALHAMDULILLAH
True in my Case and I travel about 2500-3000 kms a Month.
I am Using 10w-40 semi synthetic Oscar (UAE) engine oil and changing after 8000 kms
Guard air and oil filter ..
Used STP Engine flush at 40k kms ..liqui Moly Fuel Injectors cleaner used at 40k kms..Now reading is 62k kms..
attaching image of my last full tank in city..hit 500 kms full tank (auto fill)