Today, the gasoline is far more intelligent than we give it credit for. When there are more burn molecules in the tank, they are all talking to one another and can’t make up their collective minds about what they should do.
Therefore, only the bored ones leave the tank to do the work. This doesn’t get a heck of a lot of propulsing done. By the time you get to half a tank, their attitude changes to fear. No burn molecule wants to be the last one to get out of the think tank because they’re now talking about sports trivia. These molecules are just stampeding to get out and DO SOMETHING. The results are spectacular.
I forgot to mention the almost empty tank and the Pinto effect. That’s when the remaining burn molecules try really hard to get out and just ignite.
It sounds like you’re shifting from discussing mileage to discussing speed. Are you saying that F1 drivers keep the pedal on the floor all the way through the race?
It may be possible that premium gasoline molecules are smarter than regular gasoline molecules. Perhaps the premium gasoline molecules would behave differently and procede out of the gasoline tank in a more orderly fashion. There is probably a positive correlation between octane rating and gasoline molecule I.Q. In the old days, gasoline molecules were stupid because of lead poisoning.
I thought gasoline had mass, and therefore weight, and I thought you two (Tom and Ray) attended MIT. You get better fuel economy with the tank half empty than you do when it is full.
I do the opposite of this crazy woman. I never fill my gas tank all the way if I am only commuting. I only fill it up to the halfway mark.
Refilling your tank at the halfway mark should lower your fuel economy, not raise it. Hauling around 10-20 gallons of fuel uses more fuel than hauling around 5 gallons of fuel.
When you fill your gas tank, you exceed the capacity of the tank itself. You also fill the neck of the filler tube.
You guys are great, but I cannot believe you didn’t answer this correctly and tell Jason that his wife is wrong. The car gets worse mileage, all other things being equal, when the tank is full. It’s heavier. I agree with your answer that it does in fact SEEM that way and your answer is plausible - I’ve had cars like this. But it’s just not factually accurate. C’mon guys - give him the answer his wife wants, but then give him the complete answer so they both know what’s right!
Some of you were on the right track when you wrote about weight affecting mileage, but you were off the mark a bit.
The weight you should have considered is the weight of the needle in the gas gauge. Don’t laugh! Consider this. When the tank is full, the needle is all the way to the right (or left). As fuel is used, and the sending unit sends its signal, that needle - however lightweight - must struggle up toward the verticle. This makes it move more slowly. The length of the needle in relation to the fulcrum point varies from car to car, so different models will have more or less accurate gas gauges. Once the needle is at the halfway point, it is in a state of equilibrium. As soon as more fuel is used, gravity aids the needle in its downward fall, making it seem as if gas is being used faster than it is. To prove this mathematically, I would have to refer to one of Einstein’s equations from 1911 (which is too long for me to add here). So, I guess you will just have to take my word for it.
How would this work if, like on my car, the gauge is sideways on the dashboard? When the fuel tank on my car is full, the needle is at the top. When it is empty, the needle is at the bottom. How would this work if the fuel gauge is digital?
Your (possibly false) assumption that the caller’s car has a gauge with the needle pointing up makes your answer BOOOOOOOOOOOOOGUS.
Tommy and Ray,
You guys let poor Jason to “lose” an argument when he was correct! Yes the needle moves slower on the top half. I have a 2007 Nissan Altima with a ~18 gallon capacity. When on E, I can fill the tank with 10 gallons of gas and the needle will rise to 3/4 full. The last 8 gallons only move the needle 1/4 of the tank. I completely agree that manufacturer’s, particularly now, want the driver to believe that they get better mileage than the truly achieve. However THAT WAS NOT HIS QUESTION!!! His question was do you get better mileage full or below half, and you said his wife was correct! She did not say the needle moves faster, but that you get better mileage. She was and still is wrong! If anything you get better mileage with less gas as the car will weigh less. Clearly Jason thought, by his answers, that you get different mileage. By your confusing answer you let him get inaccurate information. You owe your listeners clarification next week. The mileage does not get better with a full tank.
Thanks
aaron
I am going to argue the opposite. You get better mileage by filling your tank less often (keep in mind the difference is minuscule). The reason is simple, there are minor losses that occur in any transfer.
As you put in fuel you may spill some, some may be lost to vapor, there are many sources of minor losses. However, if you reduce the frequency of transfer, you reduce the potential for unique transfer losses.
However, the core of the problem that the caller is having is that they have a faulty method of determining mileage. The only way to check is to keep records over the course of several thousand miles. this helps average out transfer errors and losses.
That’s very true in airplanes, especially on long haul flights. The jet fuel weighs many times more than the passengers, and fuel intake is carefully measured to just have enough left over at the destination to fly to an alternate airport if necessary.
For instance a New York to LA flight might burn 14000 gallons or so when carrying 150 passengers (average weight 160 lbs=24,000 lbs.). The fuel (assume 16,000 gallons) weighs about 120,000 lbs. or 5 times as much.
A car, on the other hand, with 4 passengers and a full tank of gas has about 85 lbs of gas and 640 lbs of people weight.
The difference between a full tank and one 1/4 full is a tiny fraction ofthe total 3000 lb+ gross vehicle weight.
a 75 lbs weight differnce in 3000 is 2.5%, and virtually impossible to measure acccurately with all the other variables.
Yes, it takes fuel to carry fuel, and in the above case 2.5% of 35 mpg is 0.75 mpg, not worth worrying about.
P.S. I am basing this calculation on ALL the loss in mileage being due to the extra weight. In reality, air resistance is the major drag on mpg at highway speed. And drivetrain friction is a major one as well, and not influenced by how much gas there is in the tank.
I still wouldn’t bother with it. Then again, I knew what I was getting into when I bought my new car, so I’ll not be one to complain about $4+ should it get here
Several posters here have gotten it right, that mileage increases as the tank is emptied and the car becomes lighter, although the increase might be so small that it would be impossible to detect in normal driving conditions. Tom and Ray only answered half of the question, explaining why Jason’s wife might (erroneously) think that mileage is better with a full tank, but they never got to saying that she’s actually completely wrong. In my opinion, they also should have more explicitly pointed out one of the obvious conclusions of their explanations of fuel gauges: that you absolutely cannot accurately measure mileage by just eyeballing a fuel gauge. You need to keep detailed records. Seems kinda ridiculous that Jason and his wife have these arguments about something they could so easily measure.
I was disappointed/unimpressed by Tom and Ray’s incomplete and misleading answer. They should repent on a future show.
The difference between a full tank and one 1/4 full is a tiny fraction ofthe total 3000 lb+ gross vehicle weight.
That’s true, but the fuel economy experts say I shouldn’t carry around my golf bag and bowling ball all week if I only use them once a week. If my bowling ball and golf clubs make a difference, so does 5-10 gallons of fuel. Some people think every little bit helps.