I have a 2005 Nissan Altima 3.5SE. The Manual says the gas tank capacity is 20 GALLONS. When the gas light refuel yellow light turns on I fill up my tank at the small line right above E. I filled up 13.702 gallons and it went past full. How is this possible for 20 Gallons if 13.702 gallons goes past full? Also does winter time with temperatures of 5-20 degrees decrease gas mileage? I'm only gettig 15.5 city.