dont mind my brother at all because by understanding you sentence i think u are search of inceasing u cars mileage .
good one yar just like me but u didnt get my piont.
again in desi language.
20w 50 oil is thicker means at running a heaviness in engine means car is not giving its optimum performance and loss of power.
and if you are only asking increase in mileage then if it gives you 11-12km in city with ac light foot then it will give you
13-14km in city ac light foot but after oil change and running atleast 1000km with new oil
means cleaning the sludge that is present on surface on the metal parts means better lubrication metal to metal contact
plus thinner oil. means semi synthetic.