Filling up gas tank - too much?

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Yesterday something interesting happened. I dropped my son at school early in the morning and then I went to the gas station before coming back home. I did the typical of topping it off a little more after the pump automatically stops. I went home and parked the car in the garage. The gas station is about 1 mile away so little gas was consumed. To make things worse, I topped the tank with 1 quart of Seafoam as soon as I got in. When I checked a few hours later there was a strong smell of gas and I saw gas dripping from the lid. When I opened the lid a bunch of gas poured out.

Lesson learned: do not top it off when is cold out there and you will park in the warm garage. The explanation I think it can be simplified with simple physics. The coefficient of thermal expansion of gasoline is 0.00095 1/C. Early in the morning the temperature was just at freezing so let's assume 0C. My garage was at about 60F (16C) or a little more. That gives me a delta temp of about 16C, which ends up being an expansion of 1.52%. Granted that the gasoline was probably not that cold so the expansion would have been a bit less, but you get the idea. For 20 gallons, 1.5% is 0.3 gallons. So it makes sense that if it was topped off that it will expand and leak through the lid. My lid is vented so I am glad it works because otherwise it would have been nasty. Doing more math, assuming that the diameter of the filler neck is 2.5" (I don't know exactly), 0.3 gallons (83.2 in3) will move 83.2/4.91=17" in a 2.5" diameter pipe. If the filler neck diameter is 2" it would be about 26.5".

If you were to fill and top off and then continue driving it wouldn't matter since you are quickly consuming some gas and the temperature change won't be that drastic so this is something to keep in mind when a sudden temperature increase occurs.

 
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Fabrice

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That's one of the things people do not stay still about. I recall having a discussion with a fuel station owner long ago,
when I went tank an exact 13 liters for my Kawasaki bike (the known max capacity) and the level was clearly lower while the exact amount of liters was displayed on the pump.
Because the rapid change in volume of fuel over here (at least at the time of this "event"), they have the distribution based on 11 celcius. Any different temperature will be corrected and thats why I did get less on a cold day. back at 11c the fuel would have been (in theory) exactly at the level I was expecting it. More by higher temp.

Stations here, and likely everywhere, get regular checks from authorities to make sure the volume price is correct a they could make lots of money in the summer as it expends.

 
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Damn Tony, if you'd know about that happening, you could have put a container under the filler, collected the gas and saved it for later and put it back in!!

 
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Damn Tony, if you'd know about that happening, you could have put a container under the filler, collected the gas and saved it for later and put it back in!!
No that much gas lost. Just a smelly garage for a couple of days and my wife reminding me of the smell every time she gets in/out of her car.

 
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No that much gas lost. Just a smelly garage for a couple of days and my wife reminding me of the smell every time she gets in/out of her car.
I only have a one car attached garage, but I got the same bs from my wife whenever she opened the house door to the garage. That was before I figured out how to tune the Holley 670 and the car always smelled strongly of gasoline. Now, I get stick when I put the car away with a hot engine. No pleasing some people!

 

Don C

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When I get gas in 5 gallon containers I have them stop at 4.5 gallons and never top off gas tanks in my vehicles. Most service stations store fuel underground and in the summer the increased quantity can be enough to cause some to overflow. It used to be common to see cars parked in the sun in hot climates dripping gas, not so much now, gas tanks have built in expansion cavities to prevent volatile vapors from getting into the atmosphere. Vented gas caps typically have a valve to prevent fuel from coming out in case of a rollover. These valves can also close and force fuel into the carburetor when gas is expanding, adding to fuel percolation problems with carburetors.

In the U.S. the standard temperature for all petroleum products is 60° F (15.6° C). All bulk deliveries have to have the quantities temperature corrected. When measuring fuel quantities in bulk tanks the temperature of the product also has to be taken and temperature corrected for accuracy.

 
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I only have a one car attached garage, but I got the same bs from my wife whenever she opened the house door to the garage. That was before I figured out how to tune the Holley 670 and the car always smelled strongly of gasoline. Now, I get stick when I put the car away with a hot engine. No pleasing some people!
Can't always make them happy. I also hear complains when there is a smell of trans or gear oil. To us that's the hot rod smell!

 
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