we have done 18k and getting 33.3 mpg avg round town, on a run it will do 38, but its all about how you drive cruising at 50 mph will give over 40, my 3 has the same engine and BHP, I managed 43.4 miles on a 160 mile journey non stop but what you gain in economy you lose in time in this case it was a full hour between Aberdeen and Glasgow. having done over 14k in the 3 now its showing 38 mpg avg.
we bought the petrol because we wasn't going over 6k per year, and I previously had a madza 6 diesel 1st gen DPF, I was only getting 44mpg and just didn't like this rising oil levels and the light came on after 11 months, dealer said it was due a service, still having 1500miles left, I wouldn't have bought the car if id known about all these dpf issues back then and its not just mazda who were suffering, but that was over 5 years ago know and I know the dpf technology has come on with different and better versions,
remember the compression ratio is 14.1 the first time I drove the cx-5 it felt a little like a diesel in that you had to quickly gear up as you progressed. you can use 6th gear a lot more than before indicator lighting up at 1800 rev about 40 mph, we have had out cx5 39 months now and its looking like we will be getting another petrol, but I would like to go see the Honda HRV first. Having said all this if you give this car some welly it really is a different beast, I managed to fend off a supercharged petrol rangie, he probably could see his fuel going down right in front of his eyes, lol. I think its one of the best handling SUV,s at speed there is for the money.