I'd echo the above. On my 20 minute commute of town driving and a blast on a dual carriageway Its usually around 26 mpg. I have taken the car on a long and relatively slow cruise and have seen around 44 mpg. I've found it to be a bit jekyl and hyde consumption wise, take it nice and easy and its very good for what it is, push it and the mpg plummets.
With regards to 95 / 99 ron fuel, quoted from golfgti.co.uk:
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Regards FSI owners mainly.
The higher the octane rating of the fuel the longer the FSI engine will run in FSI mode.
You see, when the FSI is running in 'Fuel Stratified Injection' mode it creates a lot of NoX (NoX - Very bad as far as emisions go) due to it being such a lean burn, so it has a NoX Cat which abrorbs the NoX, once its full the Nox probe (fancy lambda probe) senses this and the engine switches back to normal running and can safely clear the NoX out with the other gases through the main Cat so it can switch back into in FSI mode again.
The problem with octane levels is, and this is just an example depending on driving styles.
Out of 100 miles average :-
95RON - 90 miles normal, 10 miles FSI (lots of NoX made in FSI mode)
97+RON - 60 miles normal, 40 miles FSI (some NoX made in FSI mode)
Now regardless of what anyone says this is how the engine is built and as its more efficient in FSI mode VW always recommend the highest octane rating for this reason, they did introduce a 1.4FSI for the uk market that is made to run on 95RON fuel for longer but you want to see the size of the NoX Cat, more like a tanker. lol
And after all that, you will get better miles to the gallon running 97+RON regardless of it being an FSI, its they way they are made these days, the ecu recognises when the fuel mixture combusts and will adjust it accordingly, the cheaper the fuel the more retarded the timing, the more retarded the timing the less power, the less power the more you 'need' to put the foot down.
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The engine operates in two modes, 'power' mode and 'lean' mode (FSI). The engine will only go into lean (FSI) mode when there is no demand for power and engine speed is steady (cruising). Hence why there is such a big difference in mpg observed between the 'demanding' drives and more sedate cruises.
From my own personal experience and based on my driviving, I've found that 95 ron makes a noticeable difference to the power available at the 'top end' but its not so noticable at 'sensible' rpm's such as you might use around town and such. I would also say that for my commute i.e a lot of stop starts and basically no opportunity for the engine to go into 'FSI' mode, 95 made next to no difference to the mpg. Different story for longer cruises where the engine was able to go into 'FSI' mode, mpg was worse.
I tried 95 for about a month and came to these conclusions and am back to running on 99 exclusively.
