- Joined
- Aug 14, 2014
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- Location
- Madison, WI
- My Car
- 1971 M-Code Mach 1 w/408C stroker
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.
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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