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

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?

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.

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.

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.

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!

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 ;)

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).

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.

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.