Read up on much fuss about modern diesel being "low-sulphur", mainly to please the tree-swimming dolphin huggers.
The trouble being sulphur acts as a lubricant in your diesel pump & injectors - a deficit of this will cause premature wear & tear to an expensive pump etc...
Was told by a few others adding two-stroke oil at 100to1 (10ml to a litre) to your tank would lube the pump, make the engine a lot smoother/quieter & have other benefits??
Having nothing to loose and a handy unused bottle of Comp2 I dually added said mix to my tank after filling up at the usual filling station. A week later - this afternoon I clicked through the computer menu's to check fuel left.
My average MPG had increased from 68 to 73.2! Hasnt been above 69 since I've had the car??
My mate's went from 23.4 to 27.2 mpg ( Discovery TDV6 )
RESULT.
Try it - nowt to lose...