Yaris overfuelled?! Gasoline indicator unchanged!

Hello all, got me a Yaris Cool 1.0 VVT (newer model). Lt. onboard computer I consume in average 5.2 liters. Since the residual kilometer indicator is not really credible I do not know if the display is correct from the average consumption. Therefore I wanted to think up on the simple method how much I consume by making the tank brim full and looking how far I get with it. So I made the tank so full that the petrol already came to me, but was not an A bsicht. Now I’ve been driving 140 km without the tank showing changing. Are there still eight beams to see. Can it be that the float in the tank is broken by the overfuelling or is it actually possible to get there? The Yaris has a 42 liter tank, knows how much really fit in if you make it like I brim full? Hope you can help me further! Thank you. Dougy