Seriously I don't think you'll notice any increase in fuel consumption....however, the tickover speed is automatically increased on these when the engine is cold - once warmed up it should return to a lower speed. You should notice the difference in RPM, but so long as the van starts up hot and cold there isn't much of a problem. Cheers John
PS These aren't the most economical or quickest diesels in the world - but they are dead simple and reliable J