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Be cautious when thinking of Top Tier as a quality standard. In my opinion, it isn't.
Top Tier was set up to combat a specific issue, that of deposits forming on intake valves and fuel injectors due to insufficient fuel additives. This was some years back, and fuel companies were saving money by cutting back on detergents and other additives.
Top Tier establishes a minimum standard around the performance of deposit control additives, but it does not at all address other common fuel quality issues. Top Tier gas is arguably just as likely as any other to be the wrong octane rating, to have water in it, to have sediment in it, or to have the wrong amount of ethanol. All of the above issues cause problems with drivability.
Top Tier mandates a minimum 8% ethanol content. It depends on where you live and what the local regulations are, but where I live there is not a 10% requirement on each litre or gallon of gasoline, just a certain % requirement on all gasoline sold by a company. Consequently, Chevron can sell some fuel at 5%, some at 10%, and some with no ethanol, as long as it averages out to the minimum federal standard. The Top Tier gasolines have the most ethanol, in that example. You can guess that I avoid those, because I think ethanol is a bigger problem (for me, and my BMW) than combustion chamber deposits, given that all of the fuels I use have good deposit control additives.
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2007 X3 3.0si, 6 MT, Premium, White
Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue
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