A Question on Physics -- I Need the Help of Intelligent People

And maybe a question about chemistry, too...

So, I got this email on my listserv today. I feel like there is something wrong with this idea, but I'm not a big science wonk, so I don't know if I'm correct in thinking this. But, anyway, the email follows — see if there is something flawed in this science:

TIPS ON PUMPING GAS

I don't know what you guys are paying for gasoline.... but here in California we are paying up to $3.75 to $4.10 per gallon. My line of work is in petroleum for about 31 years now, so here are some tricks to get more of your money's worth for every gallon:

Here at the Kinder Morgan Pipeline where I work in San Jose, CA we deliver about 4 million gallons in a 24-hour period thru the pipeline..

One day is diesel the next day is jet fuel, and gasoline, regular and premium grades. We have 34-storage tanks here with a total capacity of 16,800,000 gallons.

Only buy or fill up your car or truck in the early morning when the ground temperature is still cold. Remember that all service stations have their storage tanks buried below ground. The colder the ground the more dense the gasoline, when it gets warmer gasoline expands, so buying in the afternoon or in the evening.... your gallon is not exactly a gallon. In the petroleum business, the specific gravity and the temperature of the gasoline, diesel and jet fuel, ethanol and other petroleum products plays an important role.

A 1-degree rise in temperature is a big deal for this business. But the service stations do not have temperature compensation at the pumps.

When you're filling up do not squeeze the trigger of the nozzle to a fast mode If you look you will see that the trigger has three (3) stages: low, middle, and high. You should be pumping on low mode, thereby minimizing the vapors that are created while you are pumping.

All hoses at the pump have a vapor return. If you are pumping on the fast rate, some of the liquid that goes to your tank becomes vapor. Those vapors are being sucked up and back into the underground storage tank so you're getting less worth for your money.

One of the most important tips is to fill up when your gas tank is HALF FULL. The reason for this is the more gas you have in your tank the less air occupying its empty space. Gasoline evaporates faster than you can imagine. Gasoline storage tanks have an internal floating roof. This roof serves as zero clearance between the gas and the atmosphere, so it minimizes the evaporation. Unlike service stations, here where I work, every truck that we load is temperature compensated so that every gallon is actually the exact amount. Another reminder, if there is a gasoline truck pumping into the storage tanks when you stop to buy gas, DO NOT fill up; most likely the gasoline is being stirred up as the gas is being delivered, and you might pick up some of the dirt that normally settles on the bottom.

To have an impact, we need to reach literally millions of gas buyers.

It's really simple to do.

So, break out your beakers and watch calculators, and help me find out if this is fuzzy science or not! Thanks guys!

edited 11th Mar '11 7:52:12 AM by ExterminatorZed

Both of those sound legit to me. Gas pumps dispense by volume (ie gallons) since it's easier to measure, but what actually matters in terms of fueling your car is mass (ie pounds). One gallon of gas weighs more when it's cooler than it does when it's warmer, so you get more bang for your buck, as it were. The vapor thing I hadn't heard of before, but it makes sense to me.

I can't say if either of those things will make a noticable difference, but they're at least theoretically sound.

I doubt it makes a noticeable difference, though yes, the theory sounds valid. Though I don't think the temperature of the tanks would vary all that much if they are underground...

I think I've seen some tip like this in a newspaper. Although, the paper article did't make a i deal of "a 1-degree rise in temperature". Like Tangent 128 pointed out, the temperature shouldn't vary too much if the tanks were underground.

http://www.snopes.com/inboxer/household/gastips.asp

Sounds legit, but I think the effects are severely exaggerated. Doing this might save you ten cents on gas or so, no more, imo.

I believe that subterranean structures have a constant temperature year round as long as you're below a foot or two. I think anyway, it's been a while since Heat Transfer.

I'm a bit suspect about the "fill your tank when it's half full" tip. You are after all going to be paying to drag around the extra weight in fuel all the time, and it does make a difference as well, iirc.

Well it's not that I think anything it says is outright wrong, it just seems really pointless. Like the snopes article says, how much could you possibly save by doing this stuff?

I find it hilarious that people will engage in all sorts of voodoo in the hopes of getting a few cents more petrol at the pump and them proceed to mash their accelerator at every opportunity.

As Jeremy Clarkson demonstrates here, the biggest impact on fuel economy comes from driving style. Driving aggressively will use far more fuel than driving in a relaxed fashion. And yet day after day, I see people pointlessly waste fuel by driving in an aggressive fashion.

The way people take off from the lights is a big one. I infuriate people because I take about 10 seconds longer to reach the speed limit than is typical. But when you think about it, taking a little longer to reach the speed limit doesn't really matter in the scheme of things. You can't go any faster once you're there and you'll probably be stopped by a red light eventually anyway.

But I sure do save a lot of fuel driving that way.

EDIT: It also bears mentioning that fuel is a relatively minor expense in motoring. Quite a few people think I'm insane for putting high octane petrol in my car, which is so old it doesn't even have fuel injection. However, speaking to a Holden engineer he said I wasn't completely out of my mind, because higher grade fuels come with better detergents for cleaning out an engine. And if any car needs the crap flushed out of its engine, it's an old one. My rationale there is that if I can save even one repair as a result of using higher grade fuel, it was money well spent.

edited 12th Mar '11 12:52:19 AM by TibetanFox

well I'll take a crack at it

the temperature thing seems true if insignificant but the specific gravity bit seems off.

can't say I've heard it broken down to degrees, but from what I understand it would only effect the viscosity. the rest seems more like engineering features that may or may not exits from station to station.

again, a engineering issue. but even if it's true how (in)significant the loss would be comes to mind.

I'm not really seeing the point of the first bit, what is being burned is the gasoline vapors, liquid gasoline is quite a bit harder to burn, are they really worried about the permeability of the gas tank itself?

some engineering stuff, but also wouldn't it make more sense for gas stations to be worried about a fraction of a percent or more of losses than a consumer? that percentage would be bigger for them that for the consumer would it not.

no clue what the dirt if it exists at the bottom of the tank would do to your engine however my guess would be, not a lot. especialy since it wouldn't be in tiny (or relatively big depending on the scale) clumps.

I would get out my calculator (of doom) but since it seems to be less about chemistry and more about engineering and statistics I'd rather not.

What about the specific gravity git seems off? It's just them trying to sound smart.

This. So much.

Most gasoline is used during acceleration. Driving to top speed and then heavily breaking only seconds later at a stop sign you could see is very wasteful. Accelerating needlessly in stop and go traffic (In which you will be forced to brake often) is just as wasteful and worsens the traffic situation.

The best method to save gas is to simply accelerate at an even pace (Rather then gunning it) and to coast when possible (Especially in heavy traffic, where all you may need to do is idle to figure out that using the accelerator is meaningless when the car in front of you stops in another 10 seconds). Coasting both improves the duration of breaks and can allow you to avoid needless acceleration. (I always coast to stop lights, accelerating to them then breaking is dumb imo)

It's harder on the engine as well.

That's basically how I drive. I play a little game called "use the pedals as little as possible". It results in a driving style so chillaxed I'm surprised I've never been pulled over on suspicion of driving stoned.

It is admittedly much easier to do with an automatic transmission.

One can save a surprising amount of fuel by accelerating gently and coasting as much as possible. It is what motoring experts recommend, although I'm one of the few people who bothers to read books on sensible driving written by motoring experts.

edited 12th Mar '11 2:05:52 AM by TibetanFox

specific gravity is a measure of density however it means very little in the context of a engine. It would make more sense if they were worried about specific fuel consumption, which they apparently weren't.

That was my point. They're referencing density again the same way they did before but used a different word to try and sound smarter.