My old ST220 used to get around 31mpg so between 350 and 400 miles to a tank.
Depends on how heavy your foot is, and what type of driving you do. Don't expect much. I get 20-28mpg in my ST200. ST220 should do a little better due to age of the engine. Motorway miles at normal speeds will see 350 to the tank. Don't be surprised if your in the petrol station with only 280 on the clock if you get giddy.
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