Took the car back for the 'dieseling noise' which i still had after the timing chain assembly was changed. Ended up being the mass airflow sensor. Had it changed under warranty and now am getting the normal 27 mpg around town and 34 mpg on highway. Mileage before the MAF was changed was 16 / 25. Haven't seen many issues with the MAF before.

 

I have an '08 MCS manual and I also average in the low to mid 20's. However, I live in LA and there is a considerable amount of stop and go traffic. So even though I do about 60/40 highway/city miles that basically equates to about 10/90 due to traffic. That combined with not driving the most efficient way means a loss of around 5mpgs from MINI's claims. I can confirm that good logs are possible as during long trips I'll get into the low 30's while still averaging 85 mph.

 

Update on my pisspoor mileage:

I took it in for the recall on the water pump and whilst there had them look at the timing chain as I was hearing the startup rattle intermittently.

They replaced it as it was out of spec and claim that it was to blame for the poor economy. I'm only 1/4 into a new tank so I can't tell yet.

Will update as and when I have solid numbers.

 

this may or may not be related, but my '05 reports very, very low gas milage in first gear (8 or less down to the floor at 5k+ ... might be accurate) and ~30% less than that in 2nd (about 12mpg) if I'm in 4th or higher it seems like it reports I'm getting 40+ at the same throttle setting and ~2500rpm.
The mpg meter may be bogus in other words. If you compare it to a recorded milage per "click" to full on a tank, does it match what the gauge says on the dash? Also, I found that after a year or so of not resetting the mpg meter as a previous poster mentioned, my milage went down after a s/c pulley upgrade (as I thought it should've) so you should try that again. For over a year that display was telling me I got a consistent 23.8 in nearly all city driving.

 

Ever since I did my brakes mine went down 4MPG (hand calculated from 30-ish to 26-ish). I KNOW the rears were dragging a bit at first but they seem to be ok now but it's frustrating as hell since my driving nor gas have changed.

 

Reset your avg MPG and avg Speed. it should change some. Also try some afternoon to go out for a 100% highway trip somewhere. Also, try as someone might have pointed out to calculate your mpg the old fashioned way by dividing miles driven on tank by gallons used. Also having a '10 Clubman S auto, I would recommend driving around 60-65 mph on that trip since your best gas mileage is around there. turn off your sport mode if your running that. the only time in everyday driving that will really help you is when you are around town, after about 50 its just for having fun. Since you are in DC, I would say its most likely due to driving habits (probably not dealing with winter gas). This winter I hardly got over 22 mpg. Now since its warmed up I'm seeing 30 mpg mixed again. I've seen as high as 45 mpg on highway (two consecutive all highway tanks of 93 octane gas).

 

The loaner car I'm using now (Clubman S) shows an average fuel economy of a horrifying 24 mpg. The last user must have had bricks for feet. After pumping some fuel in, I reset the gas meter and checked it at the end of the day. I was averaging 29 mpg so that's not bad for a turbo engine with automatic poking along in stop and go traffic for over an hour each day. I was expecting to average 25!