I'll take it to motorway when the running has been completed and car's driven more than 1000 KMs. Regarding Altis 1.6, on long routes, it used to give me from 15-18.7 (calculated by full tank to tank method and not by the one displayed on the MID display).
Max I got was 18.7 or 18.8 on long route but without AC and only one person in car and speed was from 80 to 90. If the car had 4 passengers and I drove it at 100 to 120, it gave me 15.7 to 16.5 KMPL.
Let's see how much of a difference Grande is going to have.