I ran for about 20-30 miles with the gauge showing empty today. If you're worried about running out of fuel then refuel within 10 miles of the gauge showing empty. If you get 40 litres in then you've got 2 litres at least as a margin

I still reckon there's a good bit of fuel left in there above 42 litres but until someone runs out or drains their tank on a forecourt (not a good idea IMHO!) then we'll never know. I was tempted to see if the 500 would make it to 500 miles but I didn't think it was a good idea with the wife in the car