Not very scientific I know but I drove the plus six till the needle went off the gauge completely after about 10 mlns got an engine hiccup pulled over and put 4 litres in and filled up about 3miles away, took 38 litres plus the 4 which is 42litres. I didn't fancy running it dry as the previous owner had it parked up for a year . So I think there might have been 4 litres left in the tank at empty. So a fill up at 300miles is achievable I think.
