Host: What time of day should I fill my tank? David Rizzo:Morning is best by far and here is why, they call it gas for a good reason. It is a gas, it expands, it is volatile. So the higher the temperature the more it fumes. You don't want fumes you want hard liquid when you put that gas in your tank. So fill up in the morning. Keep in mind that a baseline temperature is 60 degrees. For every 15 degrees above 60 you lose 1% volume. So, if you fill up on a 90 degree day you are losing 2% volume of gasoline. Gas companies say, oh, it's not that big a deal and that's why they won't put automatic temperature compensation devices on the pumps but guess what they do in Canada? They put those temperature control devices because they want the benefit of getting the volume in selling us fumes. So definitely fill up the morning.