I seem to remember reading somewhere that these days, most major brands of gasoline are essentially the same. In some areas different name brands even get their gas from the same refinery. I'm not a brand-oriented kind of guy when it comes to gas, but until recently, my wife and I would use Chevron as often as not.

About a month ago, my wife started using Exxon gas from a station newly re-opened near our house. Since then, her gas mileage has gone up 2 - 3 mpg. No new tune-ups, same daily commute, same approximate traffic conditions, same weather, same octane rating of the fuel (mid-grade 89).

Is it the gas? If it is, I'm guessing that it would be due to additives. Could they be harmful in some way? Any other ideas? I'm scratching my head.

jj
'00 2.7T
Ming Blue/Tungsten

They track this kind of stuff. As I recall, their recommendation has been to use a name brand from a busy station. Enthusiasts tend to prefer Chevron because it has Techron in it, which German makers recommend for engine cleaning.

FYI, you should probably be using 92 in your A6 per Audi. However, if you are using 89 and it works for you, go for it.

I would be amazed to see a 10 percent change in mileage when changing from one major brand to another, but there are some things that help and hurt fuel economy. Ethanol, or methanol hurt fuel economy due to the fact that they are already partially oxygenated and thus have a lower BTU content than straight hydrocarbon fuels. In a similar fashion, the more dense a hydrocarbon fuel, the greater the BTU's per gallon and thus the greater the fuel economy. Back in the "leaded fuel" days, leaded fuels offered poorer fuel economy than unleaded fuels, at constant octane, because to boost octane without lead, you needed more aromatics in the mix (benzene and toluene) which tend to be more dense than straight or branched chain hydrocarbons. The old American Oil Company (which was Amoco and is now BPAmoco) offered an unleaded, high octane fuel that was highly regarded for it's fuel economy by the people in the south and east that could buy it. It was in fact the fuel used by Charles Lindbergh to fly across the Atlantic, because he really needed good fuel economy.

As to your A6 2.7T, the recommendation is to use premium, because the engine was designed for that fuel and will give maximum performance. Even though regular may work without "knocking", the engine compensates by retarding ignition and your performance will suffer.

Hope this helps.

Sorry, I guess it seemed clear in my head...

My wife is seeing this in her SUV. I'm trying to figure out if it is safe and/or advantageous for me to use the same brand of gas in the 2.7T. I always put premium in the Audi, 91-92 octane around here.

If memory serves me correctly, I thought the car was supposed to have 91 RON gasoline. Since the octane rating is (R+M)/2 and R is supposedly ~ 4 pts. higher, the average would be 89.

Is this the case or not? Not that it matters yet, I still have until probably July before my ship has come in, literally. :(

According to the owners manual for my 2000 A6 2.7T, the recommended fuel is unleaded premium of 95 RON or 91 AKI (anti knock index, or (R+M)/2). I also says it may be operated with 91 RON or 87 AKI with a loss in engine power. It also warns of using fuel below 91 RON or 87 AKI due to the possibility of expensive engine damage.

Next time you fill up, look carefully at the octane sticker on the pump. It lists the formula used in that particular jurisdiction to figure octane. Compare to the appropriate formula entry in the owners manual. Toss and enjoy.

Other countries vary, Europe seems to use RON (ROZ) mostly.

Higher altitudes will have lower octanes, since in a normally aspirated engine, the reduced volatility is made up for by the lower ambient pressure. Unfortunately, this doesn't work for turbocharged engines.

you should be fine with any gasoline from any major marketer as long as you meet the octane requirement. In central eastern NJ, it is my understanding that 2 refineries, Exxon and Coastal, supply gas to most retail outlets, regardless of what the tanker truck has written on it. Regarding Amoco, a master marketer as an independent company before and after it was called the Ameriacn Oil Co., this was the name of the refining and marketing subsidiary of Standard Oil of Indiana. They changed the name of the whole company to better known Amoco about 15 years ago more or less, well before they were bought by BP.