How to check the average fuel consumption of a manual Santana?

Why is my fuel consumption around 9? In the city, it’s always about 10, and even after driving 80 km on the highway with moderate traffic, the average speed wasn’t high, the fuel consumption only dropped to around 7. Isn't that unusual?

I changed the engine oil from 5w30 to 5w40, and the fuel consumption increased by nearly a liter. I'm so regretful!

How many kilometers can your 2016 Santana 1.6 travel on a full tank? What's the approximate fuel consumption?