half full or half empty tank?

[spacepilot]

Originally Posted by JanGeo

Since the tanks are not insulated and are not that deeply burried then there is going to be some temperature variations in the fuel but yeah just how much is really the question.

Let's see, the coefficient of volumetric thermal expansion of gasoline is 950 10^-6/K at 20 ?C, according to wikipedia.

If the temperature is increased by 10?C (18?F), the volume of a certain amount of gasoline increases by 1% (0.95% to be exact). As a result, you are getting 1% less gas for your money, or, equivalently, the gas price is raised by 1%.

I would agree with JanGeo that the 1%/18?F ratio probably makes it worthwhile to find out how much the gas temperature can vary.

[VetteOwner]

heh good luck tryign to get a thermometer in the nozzle while the nozzles in he tank

if it were a small storage container then yea i could see it heating up and cooling off daily but those underground storage tanks are huge! (like i belive 200,000 gallons or somehting crazy) it would take ALOT of heat to heat them up so you might see a difference in winter vs summer but not on a hourly basis... and from what i know, the only scource of heat is the sun and since it has to heat all the dirt and concrete even befor eit hits the tank, alof of that heat is absorbed into the ohh, top foot at the most.(try it, dig a hole in a sunny spot and feel how cold the soil is a foot down) now imagine 6+ feet down for the tank)

that and when the trucks there dumping in the gas that its stirring up all sorts of gunk and silt in the tanks wich could end up in your tank another reason to avoid "hot fuel"

[8307c4]

Here is my experience:

1/4 tank minimum, once she's at 1/4 it needs filling, and now.
It may get better mpg but running out of fuel is not a game I like to play.

I always fill her up, the slight difference in mpg is lost when I have to refuel more often, stops waste fuel and this includes stopping for fuel. Yes, I find I can increase my mpg by maybe 0.1 by always filling up, the car gets better mpg when I can keep on going past that fuel station (unless the tank needs it).

So I am thinking, running fuel tanks below 1/2 the minor gain from the weight saved is lost when stopping for fuel (a bit of idling and then having to accelerate back to speed after fueling).

Other notes: Underground tanks hold about 10,000 gallons.
A busy fuel station has to have fuel delivered daily, at least regular.
The sediments stirred by dumping "hot" fuel stay afloat for up to 2 hours, it might help to notice if there's a specific time when a tanker truck comes in thou this usually varies.
Tanker trucks hold about 9,000 gallons.

Originally Posted by Thermactor

I only fill up my tank halfway because it's an easy 100 lbs saved. And I'm poor and dont wanna fill up the whole tank.

True, but why not prolong the interval, say if you're filling up weekly now make it bi-weekly?

[LarryClapp]

Originally Posted by theCase

I'm in the wait-till-empty camp. I personally don't enjoy going to the gas station, especially when it's subzero. Waiting till empty cuts my visits in half.

From an efficiency position, it doesn't seem to matter, but I rationalize it that it does, as one gets better mileage driving by a gas station than stopping for gas.

It is the fuel used from 0-mph to cruise speed that is wasted by all the extra stops. Why do you figure the talk about jackrabbit starts and stop signals.

The talk about half tank is all about condensation form the warmer air in tank cooling off during night forming water. "Hot air cooling creates water (ie. RAIN) Also, good idea as Northeners will tell you in Winter for heat in break-down situations, provided that motor still runs. But that puts you to 0-mpg. The other family members won't see it that way thought.
My opinion is "What ever FLOATS your BOAT"!!
My question is "Why has Other TECHNOLOGIES ADVANCED so much more over the last 100 years and yet Automobiles HAVE NOT?"

[palemelanesian]

Updated again, this time with a picture. My car has a stumble when it gets low, so the 1% column is still suspect. This is from about 500 data points on my daily commute, using the Scangauge readings. (Q1 and Q3 are the 25% and 75% points, so half of the data points are in the range between those)

[techartist]

Here's another article which might be useful to you:

http://www.creditinfocenter.com/word...or-half-empty/

[Jay2TheRescue]

Originally Posted by VetteOwner

heh good luck tryign to get a thermometer in the nozzle while the nozzles in he tank

if it were a small storage container then yea i could see it heating up and cooling off daily but those underground storage tanks are huge! (like i belive 200,000 gallons or somehting crazy) it would take ALOT of heat to heat them up so you might see a difference in winter vs summer but not on a hourly basis... and from what i know, the only scource of heat is the sun and since it has to heat all the dirt and concrete even befor eit hits the tank, alof of that heat is absorbed into the ohh, top foot at the most.(try it, dig a hole in a sunny spot and feel how cold the soil is a foot down) now imagine 6+ feet down for the tank)

that and when the trucks there dumping in the gas that its stirring up all sorts of gunk and silt in the tanks wich could end up in your tank another reason to avoid "hot fuel"

Sediment in the fuel is the very reason I will not stop at a station where I see a tanker truck in the lot, or pulling out. The fuel rushing into the underground tank can also stir up any water at the bottom, and pump it into your car.

-Jay

[R.I.D.E.]

I usually go about half a tank. With potential hurricane threats here, you could end up with no gas available for over a week. I usually stock up on gas when a storm is threatening. Last one I had 65 gallons, and actually gave some to the shelter where my wife had to work so they could have lights and coffee.

My brothers house had 2 1/2 feet of water in the living room and he had to use a boat to get 2 miles to dry land. It was raised up 9 feet the next year.

Ditto on saving the fuel pump, your tank heats up as long as you drive (return loop suel systems), so the temperature of the fuel in your tank to skew your mileage readings by not allowing a complete fill up.

regards
gary

[palemelanesian]

^ that's a good reason to keep some gas in the tank, especially this time of year, regardless of the fuel economy effects.

[KU40]

Underground tanks don't change in temperature much if at all. The sun only warms the top 6" or so. Down where the tanks are it should stay 55-60 degrees pretty much all the time. If you touch the nozzle and it feels hot it's not because the underground tank is hot. If the gas is heated up at all it's because of the pump. But most likely it feels hot because of the ambient air temperature, especially if the pump is on the end where the sun can creep onto it at certain times of day. All the ones I remember feeling were actually cold.

Originally Posted by Jay2TheRescue

Sediment in the fuel is the very reason I will not stop at a station where I see a tanker truck in the lot, or pulling out. The fuel rushing into the underground tank can also stir up any water at the bottom, and pump it into your car.

-Jay

Isn't that what the fuel filter is for?