As I understand the capacity of the US M6 fuel tank is 18 US gal according the the manual. Like most people, when the gas light comes on, I pull over to fill up. However, I find myself toping off at around ~15 gallons. So, does this mean that the car still has three gallons of gas when the light comes on? Thats a hell of a reserve....I just want to make sure I'm not hitting the crack pipe to hard 