I received this from a co-worker and while I certainly agree with some of it, not being an engineer, I can't validate the rest. But, I thought i'd share and seek opinions for some of our resident experts:
I can't imagine that the temperature of the gas in the underground tanks changes on a daily basis. At that depth I believe the temperature is pretty consistent. It probably changes slowly with the seasons, but I doubt it rises each afternoon and falls at night. Just my thoughts but I'd like to hear more on this.
I agree. I worked for a company at one time that installed the underground gas tanks and gas pumps. Once we completed an installation we had to verify the accuracy of the gas pumps by using a calibrated 5 gallon container, the same as the NC state inspector uses periodically. We would run the calibration and install the original inspection sticker for the state. We ran these tests at all different times of the day and the time of day never changed the accuracy of the pumps that I ever tested. These inspectors are travelling to gas stations all day long doing their periodic inspections. So, if there were any errors there would be some pumps failing inspections.
I think what they meant was that pumping gas in the morning would provide you a denser concentration of gas. The pump would deliver 5 gallon regardless of the time of day, the test would be to pump 5 gallons early in the morning, seal the container to prevent evaporation and then measure it again at noon or 5 pm after the gas has had a chance to come to ambient tempature. The pump will deliver 5 gallons regardless of the time of day or tempature! I do recall years ago when I first started to drive, and gas tanks weren't sealed or incorporated the evaporative return systems in today's cars, coming out to my car at noon after topping off that morning and seeing gas leaking down the side of the car from the fuel filler. So, it does expand...
Paul58, I understand what you are saying, but isn't that like saying you are going to have more gas in your tank at 5:00 PM than you are at 5:00 AM ? I think the Snopes link article gives a very good explanation on this subject. Dwight
Yep, just fininshed reading it! They do validate some of the claims, however argue savings v. time lost applying the principles may negate any real value of the practices themselves. Given the relatively small tank size in the Prius and the length of time between fill up, I still spend less time at the pump employing all these tips while filling my Prius than I spent filling my Truck and totally disregarding all these tips! Just thought I'd throw it out there for some stimulating conversation...
This is a load of rubbish. Posts like this are a social virus, otherwise known as Urban Legends. They are written to sound interesting or titillating, so unwitting accomplices continue the propagation. The only way to break the chain is to do some fact checking before you forward any information, especially anything that reads like an urban legend. Tom
The day/night temperature swings underground are very small. There is some seasonal variation winter/summer. It is true that pumps do not temperature correct their volume measurements. Gasoline is sold by actual volume, not mass, not energy content, not corrected volume. Natural gas is sold the same way. The thermal expansion coefficient of gasoline is about 0.00095 K^-1. So an 8 gallon fill 1 degree (F) colder (which would be a very large variation for day/night), nets you about .0042 gallons more, or at $3.5/gal about 1.5 cents. Not losing any sleep here. You lose a few pennies in the summer, but get them back in the winter. When you fill your tank, the air inside is displaced. That displaced air has gasoline vapors in it that are in equilibrium with the gasoline no matter how fast you fill your tank. These vapors are pulled back into the storage tank to replace the volume missing by the gasoline being pulled out. It's done to reduce air pollution. It does not matter how fast you pump. Spilling gasoline is another thing. overfilling the tank to the point of overflow wastes gas and pollutes the air, so stop at the first or second clickoff if you really do care. When the tank is less than full, the air/vapor mixture in the tank thermally expands as the temperature varies day/night. The gas cap is sealed. The tank is vented through a little can full of charcoal adsorbant to catch the gasoline vapors. These vapors are pulled back into the engine when it's running so the can will catch some more later. It gets burnt, so you don't lose any, and more importantly don't release them to the atmosphere. The can is big enough to handle an empty tank as long as you drive it at least about once per week. If you're going to let it sit for a long time, it's good to fill the tank to reduce these losses since the charcoal will eventually saturate and stop trapping. The underground tanks do get stirred up when being filled by a tanker, but the pumps have filters and water separators for this very reason.
In CA, the reason you want to keep your tank half-full (or wherever your comfort zone is) is in anticipation of an earthquake big enough to knock out utilities for an indeterminate time, but not big enough to knock down all the overpasses and trap you where you are. With a full tank of gas in the Prius, I can make it from SF to Oregon without stopping.
Kids have it too easy today. Heck, the only time anybody picked ME up was when I was wearing the cast I got when I dumped my Schwinn at 6 am while making deliveries on my paper route when my BB gun got caught in my spokes and the kid who was riding on the handlebars looked down to see what was happening and I was too late grabbing the bars. (I had my hands in my armpits before that because I was shivering in the freezing rain that Imorning.) I swear, parents these days treat their kids like little china dolls. All my mother did when I had the cast on was drive me down to the highway, where it would be easier to hitch a ride to the mine.
you forgot to add: barefoot and in the snow. to the topic: I usually fill somewhat quickly until I know I am getting close then back off and fill slowly to let the tank fill and avoid the sloshing and it gives me a better chance of stopping the fill on a dime
MythBusters is basically an entertainment show. They generally lack the scientific and engineering expertise to conduct meaningful experiments. I enjoy the show, but I also recognize its limits. Tom
