My car is almost 120,000 Km driven and I am still using 5W-30. Its a 2011 model and has not reduce oil till now. But again, I am only following the recommended oil mentioned in the manual and not an expert on oil viscosity vs total km driven relationship
In march 2017, I got an average of 18.73 in city driving conditions, but these days it has dropped to 14 km because of the increased AC usage