It is often a case of different engines and ecu . I used Millers octane boost additive in my Focus td and it increased mpg. A mate tried it in his golf but no effect. I was saving about £25 per bottle of Millers over the number of doses it gave. Basically Bottle cost about £12-13 and fuel saving about £38.
Thinking about it....was this the VW cheat fix in the ecu mapping type of effect but in reverse?
