A little Gas is a good thing...

You mean a gallon of cooler fuel weighs more than a gallon of warmer fuel right? Just making sure we're on the same page.

 

Yes, (I wrote it backwards in my hurry to go out of the door!)

BUT a single gallons weight change is almost umeasureable. Now if you were to talk about an aircrafts tanks that carries 50,000 lbs plus of fuel the difference is extremely noticeable.

The main point is that fuel does expand, go into more vapor or whatever the scientists on this forum want to call it. All aviators know this to be true from the 100 LL and Jet A fuels that stains the tar-mat at every airport.

Examples:
1).A Cessna 150, a very common high wing aircraft and used a lot for pilot training, if topped off with fuel (24 gallons) in the morning or on a cool day will drip fuel from it's tank vents during the heat of the day and if the gauges are checked during a cool morning again will not register 100% full. On average, a Cessna 150 if fueled in the coolest of mornings can place up to a gallon of fuel on the tar-mat on a very hot day.

2).Aviation fueling depots at Large Commercial airport order extremely large quatities of fuel daily and have deliveries set for "zero-dark-thirty", or after midnight - before light. They go through millions of lbs. of fuel daily and having fuel delivered in the cool of the day saves them $$$, as the tanker delivery trucks still only mehanically read gallons vs weight of fuel being pumped.

Hope this helps and now let the other skeptics step in

 

<buzzzer sound here> wrong! Cold fuel weighs MORE per given volume than warm fuel at the same given volume. It does this for the exact reasons you gave except in reverse.

example:

Aviation Grade 100LL weighs 6.3 pounds/gallon @ -40 c
Aviation Grade 100LL weighs 5.5 pounds/gallon @ +40 c

Source? EVERYTHING EXPLAINED for the professional pilot -Richie Lengel (page 384)

Basically, the reason pilots (like me) fill when it's cold is to extend my range or endurance per a given size of fuel tank. Carberators meter fuel by WEIGHT OF FUEL per volume of AIR before it enters the combustion chamber.

The reason it leaks out through the overflow vents is because as it warms up it expands and the increased VOLUME has to go somewhere, doesn't it? If you don't burn it-it ends up wasted, evaprorating in the sun after it spills out.

Lesson here: Colder = more dense = heavier/volume
Warmer = less dense = lighter/volume

Also, the realistic difference of benefit by filling up during the cold is minute (for vehicle users) because the temp at just about every gas station in the country doesn't realize a difference of -40c to +40c in a 24 hour period. Even if it did, the difference in weight would only amount to .8 of a pound per gallon.

Make sense?

Note: I wrote this before I read through the whole list of posts. I'm glad to see you fixed your goof GSM. You had me worried about you for a second.

 

In addition to my above statement: The practical reason pilots should maintain full fuel tanks is to prevent water condensation from building up in the tanks overnight and then having that water sink to the bottom of the fuel tank. If this happens, and the pilot doesn't drain the water out during the pre-flight check, the engine will quit at the worst time possible; right after becoming airborne @ low altitude and airspeed and over the least best place to have an emergency.

 

I'll see if I can find the source.

This is what I was trying to express. Thanks.

 

I couldn't agree with you more. And next time I will delay posting so that I have the time to proof read my statements while making them more thorough, and won't post while my wife is at the front door wanting to go shopping .

Either way, or at least the long way around it - I believe (with your help) we helped strengthen this point

Well time to help the other half wrap. Happy Holidays!

 

Good deal! Fly safe, man!

 

DING DING DING!! We have a winner! Haha. I agree with you entirely.

gsm, I see what you are saying. But when the conversation got started about fueling up on cooler parts of the day, i think we were talking about the tank inside the ground at the gas station and not in our vehicles. Here we don't have to worry about massive changes in temperature and pressure that you would see in the aviation field. What you are saying makes perfect sense for thousands of pounds of fuel that are in jetliners and such. Shoot i dont even know what we're debating about anymore... haha.

 

Hmmm...Makes me wonder if the FAA cares about that as much as they care about pilots dumping 2oz of fuel that they use when they check the fuel for water condensation. Crazy environmentalists.

 

ndcouch.... i'm with ya!!!!! when i die i wanna look dead!! can't live forever, i'm gonna eat what i want when i want and way too much!!

jedi.... that is the best animation ever!@!!!!

 

If there's no contamination all we do is pour it back into the tanks.

Damn treehuggers.

 

In addition to your comment:

In big airliners, they fly so high that the temperature does decrease significantly due to the temperature lapse rate of 1.98 (let's say -2 deg) degrees c/1000 feet increase above MSL (mean sea level).

Weight makes a big diff because of weight & balance calculations also.

They also don't want to carry too much fuel because the extra weight demands extra power settings to haul it...which wastes fuel.

When I fly, I don't really have to worry about temp mainly because I only work with about 15 gallons of usable fuel.

 

Liquid does not compress. Other than that you are spot on.
Hydro applications would not work if it did.
Sorry `bout the sharp shooting.

 

Lots of BS flags being thrown in this thread, thats ok its interesting..I tend to agree with the part about fueling up your vehicle while the tanker is making a deposit(stirring up crud in the storage tank..most if not all pumps have a filter though..how often are the filters changed?).I also shut the lever off to get the last few drops... and if no ones looking I might even pick up on the hose.

 

Isn't it more for calculating aircraft weight more easily (aka payload)? There is a weight penalty with carrying too much fuel. Plus the energy content in a gallon of gas changes with differences in temperature whereas the energy content in a pound of gas is constant. When you need to calculate the flying distance, you need the fuel weight in pounds. http://www.consumerwatchdog.org/resources/DPReportHotFuelUSAJune07.pdf