Dear Pakwheelers I got my toyota vitz 2015 In January it was driven 10,400km. The very first day I topped the fuel with 20 litres hobc and 20 litres of super petrol from shell, I did reset the trip A to 0 when the tank was full. After driving in city for 2 weeks (on a light foot and very less ac)when the fuel was completely end the trip A showed 640 km, before refueling I decided to change the engine oil unfortunately, I poured in toyotas 5W 50 taglon in my vitz from toyota garden motors lahore. Now I went to the petrol pump and topped the tank again with 38 litres of super unleaded and the tank was completely full till the mouth of the gauge. Did some math and got the fuel average which was with the old engine oil and hobc+super fuel 640/38= 16.8. Now again I reset the trip A with super this time drove the car for 1 week and 5 days exactly, I noticed this time that the car consumed more fuel while the driving style was same but the use of ac increased not much but a little bit this time on the trip the distance was 520km and again I refuelled 39 litres this time, the average is 520/39= 13.3, this from the day of oil change since today the car is not giving a fuel average more than 13 or 14 i even tried hobc plus super and she did 14 but no more.
Is this because of the engine oil oil or some other issue please help me sort out this and also the recommended viscosity of oil is 5w 30 can this be a reason i used desi 5w 50.