It seems that the FDII's lower gearing really starts to hurt its fuel economy at high speeds. When you've reached the highest gearing available, the only way to go faster is to spin the engine faster...
Originally Posted by Lafaso870
With *virtually* double displacement of the Pathfinder mill, the additional gasoline burden with the Pathfinder is less than 1 litre per 100km.
You can't look at fuel economy strictly as a function of engine displacement. The laws of physics state that in order to move an X kg vehicle, Y joules of energy must be used. A larger displacement engine that is able to put out the needed amount of energy with lower RPM may indeed be more economical than a smaller engine that needs to be revved way up. On the other hand, it eats up more fuel when just idling, so during conditions where both engines can keep a low RPM, the smaller one wins the fuel economy contest. And of course, when you compare two totally different vehicles, there are a whole host of variables. Driving conditions, tires, driving style variances, etc. etc. can all enter into it.
All that said, it does appear that especially with the FDII, the best fuel economy is achieved with slower speeds. I've noticed the same with my FDI - the lowest fuel consumption I get is consistently during conditions when I must keep my driving speed around 80km/h. And with the overall lower gearing of the FDII, there should be an even more pronounced difference between the fuel economy during lower speed and high speed driving.