I've tried a couple of additives in the past on different cars, with varying results. Best combination was definitely Shell Optimax with NOS octane booster on my '91 Golf GTI MK2, once the knock sensor adjusts to the fuel it was pretty potent, somewhere around 100 RON (if they both do what they say on the tin?), but that it in an older engine. I have been tempted to try the same in my Cooper, but you do have to be careful, some engines really don't like certain fuels or additives. For example my old '01 Polo 1.4 would go really well on BP Ultimate, but ran awfully on Shell Optimax.
Also I had a Leon Tdi 110, and tried some additive in that and that made absolutely no difference, maybe helped starting but that was about it, so it really depends on the engine. The fact that BMW say don't use them would make me think twice, especially as I have heard that some can even damage engines (my friend had a petrol Volvo turbo and he wouldn't go near them).
As for supermarket brand fuel, well I agree that you do get an MPG advantage with something like Optimax so that's worth extra for detergents and additives, but I've been lead to believe that standard fuels (i.e. 95 ron) all comes from the same place? |