with this modification shown on the beginning of this post
my medium consumption in the case a predominant (80%) usage on highway (130 km/h = 80.7 mph) modified (calculated based on the no. of km made between too full tanks) dropped from 6.8 l/100 km to 6.5 l/100 km ( US 34.6 mpg to 36.1 mpg). It's a 2.0 l diesel car, and I might be wrong. But even the noise level in the car changed. In good.