Would having a full tank of gas make your mpg go down because your adding more weight?

Question

Would having a full tank of gas make your mpg go down because your adding more weight?

Answer 1

Yes, but your mileage goes up as the fuel is burned off, so your mileage gets increasingly better as you approach empty. At least in theory. In reality, the difference is something you will never ever notice. Since a gallon of gasoline weights about six pounds, and most cars hold between 10 and 20 gallons of fuel, the difference between a full tank and a bone-dry tank is at the most about 120 pounds, less than the weight of an average adult. That means that you will get less fuel mileage carrying your lard-butt mother in law to her bingo game than you will carrying a full tank of fuel. You need to keep things in perspective.

Answer 2

Technically yes, but the difference would be so small it wouldn't matter.

Answer 3

The difference would be negligible

Answer 4

Yes.  There is more weight to accelerate and more rolling friction.  The amount is quite negligible compared to the weight of passengers or cargo.

Answer 5

Every pound you add to your vehicle affects mileage.  

Gasoline weighs about 7 pounds per gallon.  A 15 gallon tank of fuel weighs 105 pounds.  If that vehicle weighs 2500 pounds, the percentage of weight dedicated to fuel won't ever be more than 4% of the gross vehicle weight.