Since I got my 09 mcs mt (which is my first car) i've always been an hyper-miller. I was having bad mileage and just installed new plugs (platinium ngk's -it's probably same with stock ones) and air filter although that wasn't really in bad condition.

I recently gone for a 400km(250miles) trip with new parts with average 90km/h(55 mph). And I'm getting a mind-blowing 49mpg(4.8lt/100km). Which I believe is something really really good for a car like this.

There are newbies about topics like "how engine works" like me in this forum i believe, so this is a suggestion, if you're getting bad mileage out of your mcs(or mc) change the spark plugs first. You'll be amazed!

 

just bought a 2007 cooper s and first things I plan on are spark plugs, air filter and carbon cleaning. Fuel mileage hasn't been close to EPA but I do primarily town driving.
But first I've got to get this timing chain issue dealt with.

 

even when in-town (with average traffic congestion) i can see high 30's on my mileage.

now about that carbon cleaning, i don't think there are anyone outside the states (or maybe uk too) does walnut blasting. so i can't carbon clean my mcs. i hope it will not be a problem.