From what I have read gas mixture is not an exact science. Many factors can affect the mixture. With that in mind how do you know that the gas you purchase has the right level of cleaner in it? What if it is a little low? If you put a bottle of cleaner in your car periodically then you know for sure the engine is being maintained properly.

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[Sold] 2004 X5 4.4i - Sterling Gray - Truffle Brown, Sport, Preminum, Rear Climate, DSP, Sirius, PDC, 132's (19 inch wheel), Comfort Seats
Dynavin, JL Audio Stealthbox, Alpine PDX-5 Amp