So, apparently our filtering system leaves a little to be desired . . . after 5 tank-fulls the car wouldn't accelerate properly . . . started to get a bit sluggish. Uh-oh, we thought, now what? Oh, couldn't we hear all the nay-sayers now!!! "That'll never work," snicker, snicker, snicker, "I'll give you 3 months before you ruin that engine." Should we run a tank of regular diesel every now and then? No, we just needed to change out the primary and secondary filters... I guess a hair had got into one, and just regular gunk in the other.