So I was driving along two weeks ago and realized I needed gasoline. It was late afternoon and pretty hot outside so my girlfriend tells me not to fill up the tank as the gasoline expands and I wont get as much gas for my money.
She says you should only fill your gas tank up at night when its really hot outside. Now she is a smart gal but this seems a bit off.
Does gasoline really expand so much that you will lose money filling up on a hot day?
Well, huh. I was gonna say “no”, but after rummaging around on Google for a bit and finally Googling “gasoline expand safety hot day”, I found this.
http://www.chevron.ca/ProductsServices/Retail/HandlingGasoline.htm
So, huh. I dint know that.
The safety part I understood, but what Denise is saying is that if I fill up my gas tank on a hot day I will get significantly less gasoline than if I did so at a cooler time of day.
She may be half right. The gas is stored underground at the stations, usually, and there should not be great temperature changes day to day, so the volume you get for your $1.49[sup]99[/sup] should not be affected by the temperature of the gas while you are pumping. Ya gets what ya pays fer. If the gas were stored where it could be affected by the outside temperature, like maybe in the old days, this may hold true.
Interesting question comes from this. Gasoline does expand when heated, so does this increase your gas mileage on hot days? Are carburetors and/or fuel injectors affected by the volume or density of the gasoline?
According to this site the coefficient of volume expansion for gasoline is 950 x 10 [sup]-6[/sup]/C°. I’ll let the math mavens take it from here.
Gas tanks should not be “topped off” or overfilled because there’s a charcoal-filled pressure-vent device attached to automoble gas tanks which can be ruined/clogged when the tank is overfilled. When the pump shuts off, don’t try to put more gas in the tank.
Does it increase your gas mileage? I doubt it.
Remember, the air is also affected by the temperature, and responds by becoming less dense even as it gains volume. Engine performance in a carbeurated engine does degrade on hot days (or if you have a significant gain in altitude) unless you have a handy means of adjusting the carbeurator, which I have yet to see installed on a car.
Now, with fuel injection and the like, you have a microchip controlling the fuel/air mixture and I doubt very much you’d see any difference on hot vs. cold days.
As noted above, the petrol is stored in underground tanks that keep a pretty constant temperature. The amount of expansion that occurs in such a tank on a hot day is not all that great in most climates (an 8 degree celsius increase in its temperature will expand petrol volume by 1%.
A recent study into the issue found:
In the warmer months, sellers may gain from temperature variations, while in the colder months, motorists may gain. Over the year, the variations in volume due to temperature effects may on average cancel out or favour motorists in cool temperate climates, while working to the advantage of sellers in tropical places.
Also, the way stock is managed at the refinery has an effect on volumes. Once upon a time, fuel used to be produced at a refinery, pumped to storage tanks and later pumped into the tankers and taken to your service station. When it was in the storage tanks it had a chance to cool down (it comes out of the refinery quite warm and is referred to in the industry here as hot fuel). These days with new inventory managment techniques, refineries basically produce on demand (I’m simplifying here but stay with me), the fuel that goes into the tankers is often still quite hot and can be quite warm when it goes into the storage tanks at your local petrol station.
If you fill up just after the petrol station has had its tanks filled and if the fuel that went into the petrol station was still warm, you might be getting less fuel than you thought. However, this factor mainly works to the detriment of petrol station owners who are supplied with hot fuel that then cools in their tanks and is sold to consumers at a lower temperature.
The first problem can be fixed by fitting temperature correction devices to the petrol pumps but this is expensive and a number of studies in Canada found that this didn’t actually lead to lower prices (ibid). The second problem is fixed (at least as far as petrol station owners are concerned) by correcting for temperature at the refinery, something that will happen in Australia as at 1 December 2002
The lessson from all of this is that it doesn’t make all that much differrence but if you want to be picky then fill up on cooler days or at cooler times of the day but not just after the station has had its tanks filled.
Actually, if you fill up your car at the hottest time of day, you’ll do yourself a favor. In a place where there is a large temperature difference between night and day, a fillup in the evening could mean spilled gasoline from your tank the next morning.
~VOW
Actually, if you fill up your car at the hottest time of day, you’ll do yourself a favor. In a place where there is a large temperature difference between night and day, a fillup in the evening could mean spilled gasoline from your tank the next morning.
~VOW
Here is my take of the discussion about getting better mpg by refueling your vehicle at cool times of the day. To me the issue is will you get better mpg. Don’t think you get better mpg but you will be able to go further. That may occur if for example you take fuel out of the ground at say at 0 deg F and dispense it into your vehicle tank at say 100 deg F. After the fuel warms up it will take on a larger volume (more gallons in the vehicle tank. So if you paid for 20 gallon out of the pump (ground) the vehicle fuel tank may show 21 gallons after the fuel warms up to say 100 deg F. For normally aspirated carbureted engines this will allow you to drive further than you would normally drive with 20 gallon cause you actually use 21 gallons. Computerized fuel injected engines will precisely mix the correct fuel/air mixture say at 15:1 (15 parts of air to one part of fuel). Real good controllers actually “look” at the oxygen cause that is the stuff that combines with the fuel to “burn”. So the modern controllers do not care what the temperature is of the fuel. It measures out the amount of fuel (hydrocarbon) that is needed with the available O2 to produce a fuel air mixture of 15:1. I think the answer is you may get more for your money when the fuel is cold out of the ground and then expands when warmed up and then “burned”. You pay for 20 gallons but you use 21gallons. There is more energy in a cold gallon of fuel than is a warm gallon of fuel. Also here is a bit of trivia –a gallon of high octane fuel has less energy than a gallon of low octane fuel. Should make your head hurt……….
Ah, for the days when gas was $1.49[sup]99[/sup] a gallon.
This is the point I figured out it was a zombie.