Fill up in the morning? Myth busted, plausible, confirmed?

[aalb1]

Yes yes yes... another one of these threads... with a TWIST!

We all have heard the myth that if you fill up in the morning you fill up with denser fuel than if you were to fill up in the afternoon after it had all day to heat up, expand, and lose density.

Now the Myth Busted argument is that it isn't affected at all b/c the fuel is stored underground where the temps doesn't fluctuate as much.

But here's the twist: Costco is going to adjust "temperature adjusting pumps" in some of their gas stations. Here is the article!

So if there is enough reason for a lawsuit to be created, and the industry to start installing temperature adjusting pumps... might this myth be plausible or furthermore confirmed after all?

[TomO]

I've recently thought of this as well since it's posted on all the COSTCO pumps that they currently do NOT adjust price based on specific volume at given temps.

[zero_gravity]

if you live in canada that myth is a big steaming pile - all our pumps are volume corrected to 15?C. pretty sure thats federal law too.

i'm really amazed that this hasn't been done already in the US, theres really no reason not to. makes sure that fair is fair. you pay for the energy you buy, not the volume of liquid.

[Jay2TheRescue]

From my years of operating a service station for the gov't and a 7-11 I can tell you that underground temps are pretty stable. Our tanks were almost always about 58F. Summer/winter didn't matter much.

[dkjones96]

I always pump in the mornings because it's the only way I can make sure my pump is empty so I'm not waiting in line for a pump with 15 empty pumps right there...

Does the temperature of the fuel you are pumping ever really change tho? Those tanks are under a lot of cement and dirt.
**EDIT** Thanks Jay!

[jeep45238]

Originally Posted by dkjones96

Does the temperature of the fuel you are pumping ever really change tho? Those tanks are under a lot of cement and dirt.
**EDIT** Thanks Jay!

They do, but very slowly and not by much on a day to day basis. Go down to a basement and feel the concrete in the afternoon vs midnight

[LarryJ]

There's no question that fuel in the tank (and don't forget that there's fuel in the long horizontal fuel lines buried 2 feet below ground) is subject to increase and decrease with daily/hourly temp fluctuation. I tightness tested a few tanks many years ago and the method we used required us to circulate the fuel to ensure an even temp throughout the tank during the hour-long test. I could watch the temp of the fuel increase and decrease as the day warmed, albiet very small fluctuations.

Also consider the temp of the fuel in the line. I believe most tank systems today have 2-in dia. product supply lines that stay charged with fuel and these lines are buried just 2 feet below ground where they are subject to greater temp fluctuations than fuel in the tank. 17 gals of fuel will fit in 100 feet of 2-inch pipe. so, when you pump fuel, you may not even be drawing fuel from the tank, if your pump has been idle for some time. That's the theoretical side of it. From a practical side, I doubt the loss or gain from expansion is significant at all for each purchase.

I think the more important thing to consider is the difference between the temp of the fuel at the time of purchase versus its temp in the car's tank. Still, propably very insignificant considering the cooefficient of expansion for gas and the small amount of fuel pumped (less than 10 gals in my VX).

[JanGeo]

So what you want to do is get gas when they have just filled the tanks on a cold day so the fuel is chilled in the tanker truck on the way to the station.

[Jay2TheRescue]

Wrong answer... NEVER purchase fuel if you know their tanks were just filled. Any water and/or sediment in the tanks can be pumped right into your car! If I see a fuel truck in a station I pass it on by.

[GasUser]

Originally Posted by Jay2TheRescue

Wrong answer... NEVER purchase fuel if you know their tanks were just filled. Any water and/or sediment in the tanks can be pumped right into your car! If I see a fuel truck in a station I pass it on by.

Yup, me too.

And I thought it was just me being anal since everything is filtered.

[JanGeo]

Guys! come on, unless your station has the fillers in a hole where rain water collects, the fuel is going to be clean - the amount of fuel being pumped through a tank is so large that the chances of there being anything but gas in there is infinitesimal. Any water will be absorbed by the ethanol and in fact the fuel should contain less moisture than that which was in the tank for the past week since it is fresh. You are actually better off with a load of fresh gas since it is cleaner and the sediment (if any) hasn't had a chance to build up and concentrate towards the bottom of the tank near the outlet as the tank level gets low. Besides what are the chances of you getting fuel JUST AFTER the truck filled it up.

[Jay2TheRescue]

I have seen stations where rain water would fill the holes where the tank fill holes were, but all stations have water in the tanks, its just a question of how much. Condensation forms when fuel is pumped out of the tank it is replaced by air. This air has water in it. When it cools the water condenses on the walls of the tank and falls to the bottom. I have never seen an underground tank that didn't have some amount of water in it.

[JanGeo]

That said then the ethanol gas blend in a near empty tank would probably be saturated if there was standing water in the bottom of the tank. Ok then your arguement for it getting mixed up upon filling is somewhat valid but also 1000-2000 gallons of fresh gas with 10% dry ethanol would soak up a lot of that water when mixed into the tank. Although water in the fuel can cause corrosion it can also aid in combustion like water injection.

[Jay2TheRescue]

When I worked for 7-11 in college we sold E-10, and I know there were no leaks because I checked the tanks nightly and did the fuel reports myself. Our tanks normally had 2 -3 inches of water in the bottom of the tanks. Same when I worked for a fuel station operated by the USMC. No leaks, but there were always a few inches of water in the bottom of the tank.

I just don't like the idea of water in my tank. At the very least any water pumped into your tank has displaced gasoline, and you paid $2/gal for water.

-Jay

[trollbait]

You are assuming the ethanol is dry to begin with. It takes more than basic distillation to get absolute ethanol, and even then, it will gather moisture from the air if not stored properly.

Do they start with absolute ethanol for auto fuel? Or is the trace benzene big enough deal not to?

[JanGeo]

From what I have read about the ethanol process they get it pretty dry with a final stage to absorb most of the water out of it.

From what Jay is saying I guess I better not be gassing up after they fill the tanks - hard to believe that much water would be there but then again that is the problem with vented tanks. You would think they would have some way of constantly draining that water out from the bottom of the tank. Makes me wonder if the initial increase of MPG with acetone was from the water in my gas tank being absorbed into the fuel and burnt as a combustion enhancement.

http://en.wikipedia.org/wiki/Ethanol_fuel
Wiki had this way down on the page . . .

"With increasing attention being paid to saving energy, many methods have been proposed that avoid distillation all together for dehydration. Of these methods, a third method has emerged and has been adopted by the majority of modern ethanol plants. This new process uses molecular sieves to remove water from fuel ethanol. In this process, ethanol vapor under pressure passes through a bed of molecular sieve beads. The bead's pores are sized to allow absorption of water while excluding ethanol. After a period of time, the bed is regenerated under vacuum to remove the absorbed water. Two beds are used so that one is available to absorb water while the other is being regenerated. This dehydration technology can account for energy saving of 3,000 btus/gallon compared to earlier azeotropic distillation."

[Jay2TheRescue]

The problem is you just can't drain it off. Water that has been in contact with gasoline is considered hazzardous itself. We had to have it professionally pumped out and sealed in 55 gallon drums to be hauled off by a disposal company.

[shatto]

I suspect this is being done because their attorneys recommended being proactive because some jerk will try getting some money from a lawsuit.

Costco sells a huge volume of gasoline. My store sells at least 30,000 gallons a day. Sometimes there are two delivery trucks there at the same time.

This translates to all the fuel being at pretty much the same temperature and I don't imagine that much cooling takes place the nine hours the station is closed.

[101mpg]

With YEARS of data I can tell you conclusively it is NOT a myth. You need to have big differences in temperature, however. If you live in the desert, Southern California, or other places where it gets pretty hot and the daily temperature variance can be 30-40+ degrees, it is TOTALLY true. It is NOT a myth.

Filling up at a station where they have just pumped in gas and it has not had time to settle WILL put crap into your tank. Sediment gets stirred up, it goes into your gas. You think they filter down to one micron? Hardly. More like a colander trying to catch sand - which doesn't really work.

Winter months, days with much less temperature variance - this will not show much if any difference in MPG, but large temperature variance over the day WILL show better results if you fill up in the morning. 6 am is best in the summer. Myth CONFIRMED. Anyone who says otherwise hasn't checked with the right variables.

The reason the US companies have not gone to temperature adjusted pumps is because it makes no monetary sense for them to do so. More customers in daylight hours with expanded gasoline, more money. Why would they do so voluntarily? Most won't, and only will do so if forced.

[VetteOwner]

i dunno about my area (maybe changed 20 degrees from daytime to night temp)

but i had to fill up 15 gallons and after it was done the pump nozzle was ice cold when it was 70F out (i filled up at 5pm too)

so for my area i really dont think it makes a whole lotta difference....(that and our stations have those huge pavilion so you and the pumps are always in the shade)