---- OlRivrRat <OlRivrRat@COMCAST.NET> wrote: 
>          Also keep in mind that the vol' of a  
> Gal'OfGasoline @ 80º is 233.7CuIn
> 
> & @ 30º it is 227.0CuIn so you actually have less GasByVolume in your  
> tank in the Winter
> 
> than in the Summer but I haven't really thought through what effect  
> that might have on

Hmmmm........... .  Do you mean that a gallon is not always a gallon?  Is the gallon you cite a gallon at standard temperature and pressure (O C,  760 mm Hg) but a bit bigger at warmer temperatures?  Because a gallon is a measure of volume.  The fuel may expand and shrink, but then it won't be a gallon any more, it'll be something else.

Now, if you cited a variable volume for a given mass of fuel (again, the weight but not the mass could vary depending on where the measurement was made), then we'd be getting somewhere.  If you want the same exact amount of fuel regardless of conditions, you need to deal with mass, so as to have the exact same number of molecules.

If you put in a gallon of fuel at one temperature, then the stuff expands as it warms up, there is still no more fuel in the tank, it just takes up more volume, more than a gallon.  Same if it shrinks, it now takes up less volume, less than a gallon.  The amount of fuel does not vary, just the space it occupies.

If you buy a gallon of fuel that is cold, and another time buy a gallon of fuel that is warm, the second time you get less fuel.

All this would suggest that one might get better mileage (miles per gallon) in winter, since by burning a gallon of fuel, one burns more fuel, but other variables seem to obviate that.  At least they do for me, as I get poorer mileage in winter, by subjective judgement, anyway.  Of course, to be sure, we'd need a controlled experiment that is probably beyond our ability to design and carry out given the limitations of available vehicles and ability to control variables.

mcneely