Gas shrinkage?

[jwxr7]

Lets say I fill my tank in 40 F weather, I'm still driving on that tank but now it is -10 F. Will it be a noticable change in volume? If so, then isn't that going to neg impact my FE for that tank, or is the denser gas going to "go farther"?

just wondering because it seems like my gauge dropped extra fast.

[SVOboy]

Gas will change volume, slightly, perhaps, some argue not enough to be noticable. I don't know for sure. But it's unlikely to cause a noticable drop in fuel economy.

[DaX]

The volumetric coefficient of thermal expansion for gasoline is about 950 x 10^-6 cubic meters per degree C.

[Peakster]

Allegedly it is quite noticeable. My Physics teacher once said that tanker trucks, when going from a hot location to a cool location, will suddenly have hundreds of dollars of less fuel than when they started out with if absolute volume was taken into play. This is why all the gasoline pumps I've seen declare "all volumes corrected to 15*C" to make sure everyone is paying the same price for gas.

There's been a few times where I'd fill my tank to the brim, drive around doing some arrands, and park my car in the garage. The next day, I'll try using a fuel additive and when I open the gas cap, fuel spurted everywhere!

[jwxr7]

DV = bV DT (D is delta, b is thermal expansion coef, V volume, T temp)
If DV=.0095 m^3/C x .02712 m^3 x 27.78 C (.02712m^3 is 6 US liquid gallons of gas in tank, 27.78 C is change in temp) then my fuel changed volume by about .0005994 m^3 or .15835 US gallons or about 20 oz of gas. That could be equal to 8 - 8.5 miles of driving.

Probably not noticable with the fuel gauge.

[MetroMPG]

Originally Posted by jwxr7

That could be equal to 8 - 8.5 miles of driving.

Except the amount of energy in your tank doesn't change with expansion/contraction.

[jwxr7]

true, but does the engine actually get more energy when it burns the denser fuel or is it wasted by being too rich? May depend on car and state of tune.

[DaX]

Originally Posted by jwxr7

true, but does the engine actually get more energy when it burns the denser fuel or is it wasted by being too rich? May depend on car and state of tune.

This is why cars have o2 sensors - to compensate on the fly for this.

[MetroMPG]

I suppose it could have been true in the days of carburetors. Or pre o2 sensor FI (my old Rabbits all had FI, but I have no idea if they also had o2 sensors...)

[JanGeo]

I read in the Synlube site that gasoline expands and contracts about twice that of water - just looked for a while and couldn't find the actual numbers however. You still have the same BTUs that you bought at the pump - but you should buy the gas right after a cold snap to get it at its coldest temperature at the pump. Just be careful of expansion as it warms up.

[jwxr7]

I guess I won't use shrinkage as an excuse for lower FE #s.

[diamondlarry]

One day last summer, I decided to make some FE test runs so I drove about 6 miles to the station and filled up. I then drove about 25 miles or so and went back to the same station/pump and refilled. After squeezing as much gas as I possibly could into the tank, my mileage figured out to be way over 200 mpg. Apparently the fuel expanded enough to cause the mpg to be way off.

[lunarhighway]

mmm

my car sits outside all the time and has a carb... yet these days despite the temperature flirting with freezing, once my car is warmed up it actually seems to drive a bit sweeter than usual... i thought it might be because it was getting more cold air, but could it just be that it's getting a richer mixture because of shrinkage?... i seem to require less throttle than before to attain a certain speed. could be something else of course....

this could alse mess up my gasslog as i have to resort to the "fill up to the brim at the same fuelpump" method to calculate my FE...

[Matt Timion]

[Peakster]

Originally Posted by diamondlarry

One day last summer, I decided to make some FE test runs so I drove about 6 miles to the station and filled up. I then drove about 25 miles or so and went back to the same station/pump and refilled. After squeezing as much gas as I possibly could into the tank, my mileage figured out to be way over 200 mpg. Apparently the fuel expanded enough to cause the mpg to be way off.

He hehe, it would be nice if one could get 200mpg+ every time a car was filled 25 miles later

[JanGeo]

Yup a second tank in the back of the car using a 45 liter beer or soda keg stainless steel and plenty of them around strong and able to withstand plenty of pressure. Top it off when the gas is cheep and pump it into the main tank when you need it.

[skewbe]

I could do with a smaller tank, ~6lbs a gallon and I haven't come close to running out yet, so I'm probably carrying an extra 30lbs or so of fuel I don't use.

Maybe I can inflate something neoprene in my tank and pull it out before a trip?!?