My wife tells me cars get better gas mileage when the tank is at least 1/2 full. She claims it has to do with pressure in the tank. I maintain the amount of fuel in the tank wouldn’t have much to do with it compared to driving habits, etc. and possibly the less fuel in the tank, the better gas mileage (less weight of the car). Please help us solve this question before things get really ugly!
:smack:
My intuitive understanding agrees with you, but I don’t know much about cars.
Gas gauges lie. When your tank says “E”, it’s not really empty. Depending upon the make/model of your car, you can still probably drive for quite a while with the gauge on “E” before the “Low Fuel” light comes on. Car manufacturers deliberately make the gauges inaccurate once they drop below half a tank, that way you’ll be more likely to stop and get gas before the tank runs dry (which can really screw up some fuel injected cars).
You are right. Your wife is wrong. Good luck explaining it to her.
What sailor said. The pressure is completely irrelevant in any practical application. Moving that extra mass of fuel around is takes some effort. But at only about 7 pounds per gallon, it’s nothing compared to the effect of having some hulking behemoth of a man in your car. ::shudder::
Hey! I was having a bad day.
You are right. After you goad her into a substantial bet , here’s what you tell her: If it’s a carbureted car, the fuel is pumped to the carb, where it’s under atmospheric pressure in the bowl. If it’s fuel injected, the fuel pumps the fuel to the fuel pressure regulator, which keeps the fuel at a constant pressure of 43.5 psi above manifold pressure.
This is all speculation and “if-I-recall-correctly”:
The longer you drive on the highway non-stop, the more the aerodynamics are important and the less the mass of the car. (I.e. in stop-and-go traffic, having as little mass as possible yields the least energy to get to a particular speed, but on the highway, only the shape of the car matters.)
Depending on the car, it could be lowering the suspension in the rear enough to improve aerodynamic drag. Old station wagons were notorious for this where their aerodynamics improve if the back end is lowered, yielding a sutpid looking car but with better mileage.
You must know my wife!!!