I bought my 2010 Cooper non-turbo back in October, and since the start the actual fuel mileage (as measured, not based on the computer) has been surprisingly low. Normally it measures in the 33.x range, but it has been as low as 30.x without any obvious explanation (no extended idling, no racing or extreme driving). I replaced the spark plugs, both oxygen sensors, the air filter, motor oil and filter, and the transmission oil; nothing seemed to improve it. I had been using Mobil gas (93 AKI) exclusively since it's plentiful where I live and a top tier gas. One day on a whim I filled up with Sunoco 93. My fuel mileage instantly started climbing. The next time I filled up I measured the first tank of Sunoco to be in the high 34 MPG range. A tank full of Shell achieved the same. A subsequent tank full of Sunoco achieved the high 36 MPG range. A change from 33 MPG to 36 MPG might make one think it could be down to the subtleties of driving style, and while I admit it's possible, because of the uniformity of my driving I really feel like that's not a significant factor.

Has anyone else experimented with different brands of fuel, or accidentally discovered a brand they like best based on how it works in your car, rather than just personal preference/bias? I think I'll experiment with the top tier brands available to me, see what I can learn.

 

I've seen it around here, generally a couple mpg difference between brands.

Nik

 

The best way to get a true read on MPG is over a longer period of time. Try averaging after say 10 or 15 tankfuls of the same brand AND octane then do the same with another. Consistency is the key. To a small degree, weather conditions and changes in barometer can also have an effect.

 

Also they have different grades or quality of gas from season to season, station to station. I driven allot of miles and have not seen that much change in mpg, but i choose a tier one supplier for fill up almost always.

Sometimes when you notice a big change its not due the gas but the O2 sensor on its way out before the CEL, happened to me twice on my R52.

 

Especially so if your state has a mandated "winter" blend.

 

Winter blend here in the midwest is usually good for a 10% drop in fuel economy. Despite that, your right foot and driving habits have a much bigger impact than varying brands of fuel, most of which get their goods from the same distributor.

 

I only noticed I would lose 2mpg when going to Rotten Robbie when I had my Civic. I only put Shell, Valero and Chevron into the Mini and the mpg seems the same.

 

Yea, we have that.

 

Winter blend fuel, colder air, colder engine, colder tires... All sorts of things make your mileage worse in the winter, and better in the summer. If your weather has taken a turn for the better, that could easily explain the difference.

Driving style can also make an even bigger difference.