Just thought I'd share this. I've been using diesel Redex and two stoke oil for the last few months (both from Wilko's, £2 for the Redex, £3 for the 500ml T2 Jaso FB grade) both will do two full tank fulls and have been achieving a consistent 10% improvement in economy and a much quieter cold engine and more responsive when booted. My daily trip to work (at 10 miles from home) is now 47/48 mpg up from 42/44 mpg (and much less sometimes). Can't explain why maybe its acting as an upper cylinder lubricant and decoker but it works. Might take a tankfull before the benefits. Non dpf car by the way (CLK 270 CDI). Cheaper than silly priced diesel 'super' grade per fill up and it works. Redex and 2T, try it.