How much weight does a full tank of gas add to the car? What do we carry, about 15 - 17 gallons full at any given time?

Just wondering because I've raced a couple of cars on the street recently and for one I had a little less than a quarter tank, felt good. But the other was when I had just filled up the day before, and the car felt a little bit slower getting into 4th gear. Does the added weight make much of a difference?

 

a gallon of gas weighs 8.66 lbs at room temperature

 

so if you have 10 gallons of gas in your ride--your looking at an additional 86.6 lbs.......as opposed to 17 gallons of gas----an additional 147.22lbs.....AT ROOM TEMP OF COARSE...

 

That's like an extra person

 

Its Gotta Make A Difference...even If Small...every Lb Counts...

 

you know you gotta problem when your g/f weighs more than your gas!!!

 

It absolutely makes that big of a difference. I heard that a gallon of gas weighs seven pounds but what beetroot said may be a little more accurate, I didnt take into account the temperature.

The gas would get heavier as it gets colder, correct? or the other way around?

17.3 (tank size) * 8.66lbs (weight of fuel) = 149.818 lbs.

at a quarter tank you would be saving:
17.3 \ 4 = 4.325 gallons of fuel * 8.66 = 37.4545
149.818 - 37.4545 = 112.3635 lbs

 

74.909lb difference....

 

They say that an extra 100lbs will cost you a tenth of a second in the quarter...

 

if thats true then this is damn close to costing someone a tenth of a sec....i guess its more of a difference then most people ever thought...*not much*..but more than they thought..(or at least more than i thought)

 

Always race on E!!!!!!!!!!!!!

 

Gas is only 6 lbs per gallon!

Water weighs 8 lbs per gallon.

 

http://www.madsci.org/posts/archives...1745.Ch.r.html

 

you are correct. 6.2 - 6.3 depending on the grade according to a google search.

I ruined this thread.

 

way to go Beet you ruined my day and all those calculations I made.

*all hail beet, the day ruiner*

 

Wait how would the same amount of gas weigh any different at different temperatures, in a sealed container?

 

Same way air in a sealed tire will have more PSI when hot than when cold; heat expands and cold contracts.

If the gasoline is contracted and cold, it will take more to fill a one gallon container, just like it will take more cold air to fill a tire to say 35psi .. but drive those tires hard and I bet you'll see the air pressure at around 40psi, then when they sit and get cold it will drop back to 35psi.

 

= Rootbeer

 

Rootbeer = DOH!

 

 

This is completely untrue. The reason it works that way in tires is because that gas (air) is a gas, not a liquid (gasoline). Liquids DO NOT compress the way gases do....the VERY small amount that a liquid does "compress" is so minute that you could not tell any difference unless you had analytical chemistry equipment....and you don't.
This is why hydrolock happens. While gasses (air, nitrous, etc.) can be compressed in a cylinder, when water gets in a the piston tries to compress it, the piston loses.

In effect the difference in weight for a liquid at difference temps is so miniscule that it makes no difference.

 

it makes a big difference when you put your beer in the freezer and it expands and blows up all over the place

 

made me laugh.... The beer actually compressed a minuscule amount for each degree colder right up until it hit 32 degrees F, then the phase change to a solid is what expanded it quite a bit.

Is it easier to clean the freezer if you leave the beer splatter frozen, or do you have to defrost?

 

The crystalline structure of water when it freezes makes it lose density once it reaches 32F. But that is ONLY with water.

And I believe that scraping frozen beer is easier than soaking up the liquid....IMHO

 

Oldest racing weight saving trick in the book.

 

god.. i always forget why race cars always have fuel cells.. maybe cuz it looks cool?

 

 

You need more than 2 cents. You need common sense. And, you have the nerve to comment that the previous post is

You need to get some facts straight and/or at least head back to class before spewing out this drivel as fact. Thermal expansion has nothing to do with compressibility.

There is a very real test that you can try one day: fill up your car in the AM with cold gasoline. Make sure it is really cold and the car is dead cold. Make sure to fill the tank to the the very top and leave as little free air as possible. If you have a really cold days, where the morning is really cold and day very hot -- as occurs in some of our local desserts -- let the car sit in the sun (the idea being to not consume any gasoline while the car bakes); you can get a lot of pressure to build up in the gas tank. The math follows in a section below.

Pundits and gear heads have recommended getting gasoline during the cool morning hours for years. You get more gas for the $$$. AS the exhaust and other components heat up, the fuel expands. (This advice can be tossed if a comet hits the earth causing eternal winter and/or earth’s orbit moves out to Uranus.)

Here’s a little excerpt you might want to consider. Liquids and solids expand. The amount of expansion is very important because they ARE NOT COMPRESSIBLE!!!! You should consider that structures, containment vessels, and systems that use liquid and solid materials need careful design with respect to temperature swings due to the relative lack of compressibility.

LINK: Temperature and Heat

There are dissimilar rates of thermal expansion of the gas tanks solid material and the fuel (liquid). If the tank was sealed, there would be a chance for explosion, cracking, or leaks if an overflow and/or pressure relief valve or other means of fluid escape weren’t provided. The gasoline is isotropic as are homogenous steel alloys.

Compressibility has NOTHING to due with thermal expansion. Your analogy is misguided and inappropriate. (If you want to get into the fine points of compressibility in solids, liquids, and gasses, go right ahead. There are liquids that are compressible. One example would be: water with high levels of dissolved oxygen; it has limited compressibility. If you look at fluid dynamics or simulation tools for Computational fluid dynamics, you will see that there are provisions for “compressible fluids” for use in various models and tools.

Mercury is a liquid metal and it expands quite nicely. Get a mercury thermometer and get ready to dismiss the idea the thermal expansion is “so miniscule” that it makes no difference. Heat it up past the top of the column and watch it burst. Just make sure it doesn’t get all over you.

 

This is all fine and good...but a few problems -
The temp in the problem above does not change....how can thermal expansion come about if there is no change in kinetic energy in the system?

I said the change would be miniscule is terms of WEIGHT!! Even in your screwed example, the weight change from him losing 0.51 L is less than 1% of the weight of the gasoline....how does this make any difference in the weight in his tank?

Figuring this tank, at 56L (~2.2L/gal and ~6lbs.gal) weighed 152.7 pounds full....his tank after expansion and spillage would weigh 151.3 lbs. ( a difference of 1.4 lbs. or 0.009%)

And this is not going to be a tank which gets filled "to the brim".

Besides, we are talking about weight of the gasoline in a car. Whether it is in the sun at 100C or in -10C Minnesota weather makes no difference in the weight of the gasoline, being that the same amount of gasoline is in the tank, it's molecular "connections" have simply changed it's density(which I believe was the point of the first post)

You're obviously more well read in physics than I (a molecular biologist), but that doesn't mean a bad physics hypo will change the fact that in this isolated case, I know a little physics. I will, however, concede the rest of your points regarding thermal expansion, with the exception of Hg. Mercury is a weird element, it has no place in the periodic table. I realize what it is and that it occurs, but saw that the issue was not expansion, but rather compression of gas v. liquid (as Bladder discussed in his post).

 

 

Yes, there is a typo in the pdf file. The ΔT is 10-degrees C. Adjust the figures as you please (IOW, make the gas station 0°C with garage at 10°C or change the text to read, “…and the heated garage hotter by 10°C."


Here is the math to verify this:

950*10e-6/K * 0.056*m^3 * 10°K = 5.32 * 10e-4

So, let’s take this a bit further and change the ΔT difference from 0°C to 30°C. IN Fahrenheit, it would represent getting your gas at 32°F (0°C) relative to 86°F (30°C). Change in temp = 30°C or 54°F

If you simply use change the 10°K to 30°K, you’ve increase the relationship by 3x. IOW, you now have a 3 percent difference and the fuel can easily get up to 130 degrees in the gas tank. I’ve gas temps in my Bimmer in this range (the final exhaust can sat right next to the tank -- it got really hot!) Look below and you'll see you miscalc'd the percent by a factor of 100

If you look at the back of your car, you will see that there is an exhaust system sitting right under the gas tank. If you heat it up, entropy increases, you get thermal expansion.

I could continue. You need to look below and realize that the pump is measuring the gas VOLUME. When you deal with volumes, the weight is important when viewed in context. (See and read the section below regarding flow meters, etc)

You need to watch those percent calculations. 56 liters relative to 56.5 liters is NOT a difference of 0.009 %. Your off by a factor of 100

56 / 56.5 ~= 0.98 % (IOW, 56 liters relative to 56 liters + ~0.5 liters is approximately 1%)

If you want to quibble, you could argue that 1% is miniscule. If you were in F1 racing and said the 1% was miniscule, you would be handed your head and the same can be said for a number of physical science pursuits. You don’t need any specialized gear to measure a 1% difference (1 part in 100).

You’re still missing some key concepts: (pumps use flow meters; they don’t distribute fuel by weight).

The pump dispenses the fuel using flow meters. It does NOT weight the fuel going into the car. If you visited the pump at the end of the day – when it was warm or hot – and let’s presume that fuel’s temperature was equal to the temperature of your warmed-up car’s gas tank, you would get a fixed volume of fuel that would not change (this provided the temp of your tank stayed constant – it doesn’t). The gas pump would read 10 gallons (or whatever), but the volume and density of the gas would change with temperature. So, if you now went into the station and purchased the same 10 gallons of gas, but with the gas temperature being icy cold, the gas pump would still “register”/"report" 10 gallons delivered on the pump's display, but due to its higher density, it would really have a higher weight relative to the gas you purchased that was hot/warm. So, if you want to forget about the issue of tank overflow, you still need to understand that the 10 gallons you purchased COLD would weight MORE than the 10 gallons you purchased – at the end of the hot day – that was hot.

Your very own comments should finish this discussion off by considering that the pumps in both cases say you’re getting 10 gallons, but the volume that was delivered would not be equal due to the density and measurement by volume. And, since gas is measured by volume, density impacts weight, and this is not unimportant. Even race teams will cool gasoline for a small advantage (in a number of areas).

Remember, the molecules are in motion, they are not as energetic as those in a gas, and the term compressibilty is relative to some extent. If the entropy is higher, the molecules are in a higher energy state and the number of molecules in a given volume is lower.

One example: DOT 5 Silicone fluid won't absorb water and I've used the stuff. However, the compressibility, why nothing close to a gas, was enough to create enough "give" in the brake pedal to be noticed.

 

thanks, I understand that. He was not talking about when you get it, but rather how the same amount would change over the day in your car....


I guess it's a good thing that I'm a biological scientist, huh? I did all of the analytical / physical chemistry in UG, and found that they mostly are based on fantasy (all of the theory is based on an utopian ideal of factors, none of which are realistic). One reason of 230,000 that I didn't go into engineering (did I mention I also went through UG and a MS without taking Calc?? )
Also, If I was in f1 I would not be hanging around a CL board.
You do realize that gasoline is held ~8 feet underground, meaning that even if you started a day at -10C, and somehow got up to 30C, the gas would not heat that much before you filled your tank.


Yeah, i understand that (see density description above). My ENTIRE point was that the weight of gas does not change over a day whether a car is warm or cold, and that the change in gas you get from those temps is unimportant to the original question pondered. Show me a hypo that is somehow related (unlike your F1 hypo), and we can talk. These hypos do nothing for your argument.....since mine was predicated on us driving Cl's, not 1500hp machines.....


...again

 

there is one D in my member name

 

you really like that smilie.....or really dislike me.

 

JaredGMS

How To Save


Gas is not only in the ground. The pipes are above ground, the pump is above ground, and a number of objects that store the fuel are exposed to ambient temps and solar radiation. IOW, stuff gets hot above ground. Not only does this heat the gas in the ground as it exits, there is also a variable volume of hot fuel that is sitting in the pump and lines.

Also, I've pumped jet fuel out of the ground in winter and it was cold enough to freeze my hands.

The tanker that delivers gas is not underground, if it shows up during the night, or first thing in the morning -- a not uncommon event for my local station -- the gas is going to be COLD relative to an afternoon delivery. The tankers are NOT refrigerated!

This is old news…

You also have reframed your arguments as each posting has gone along with your deciding what is hypothetical, relevant, and I really don't care. You posted-up some incorrect information and I pointed out the physics involved with hard calculations.

You have either a poor way of expressing yourself, or a lot of audacity to "determine" what is worthy enough to talk about.

A lot of little details add up.

I'm just going to have to disagree with a number of your conclusions and opinions above.

Finally, to get back to the original reason I commented:

IMO, specialized analytic gear is not equivalent to a cheapo scale, gallon jug, and thermometer. And, that’s all you need to determine the weight change of gas with common pump temp changes.

 

You don't care, and yet you feel like you still need to respond to my poorly expressed, audacious arguments. And your "hard calculations" were based on a hypo with incorrect information....
He pointed out a gas v. liquid argument for pressure, and I thought I corrected that. You brought up hypos for thermal expansion that really have no application in our cars.






How about :padlock:

 

 

I realize that is simply an artifact of the effects of living in NJ.....



BTW - Go fuck youself

 

What weighs more 10"0000 of nails or 10"0000 of hay?
what weighs more a gallon of water or a gallon of gas?

 

thats why ya hit the track with less than a 1/4