How much liters of eurodiesel requires a Megane 1.5 dCi (80hp) engine while it carries the car at a ...

Hard to say, depends on engine condition, etc.

Yeah that's important, so I need to explain the condition. The engine's kilometer age is 65.000 km. and I have taken care of the engine in every 15.000 kilometers in an official Renault service. Well, the answer of the question hardly changed for three years since I've  bought the car.

Fixed speed of 190 kph with 1.5 dci 80hp ? Impossible, max speed is about 175 kph. Sorry, you'll need the 1.9dci for this... (if i remember well 190 kph = 12 liters/100 km with the 1.9 dci 130hp...)

You're absolutely right, I know that the Megane should barely go at 175 kph but I saw the kilometer display at 190 kph however I am not sure of the conditions of the highway but I can tell you that it was windy from sides and I wasn't climbing. But I heard from an expert that the kilometer display always showed the driver %10 more in compact cars and even much more in smaller cars because of security reasons. I tried to make a photo if the speed display but the photo is really in bad quality because of shakes. Anyway maybe the kilometer display was fooling me :) So in both cases 175 or 190, it needs 9.6 liters.

Thank you for your reply!

By the way, check that photo, from 'My Cars' section.