On another related cold-weather engine subject is gas mileage, or more correctly gasohol mileage. Alcohol-blended fuels do not have the same BTUs (British Thermal Units) as "pure" gasoline (IE, gas with NO alcohol in them). BTU are the physical measurement of the amount of heat that will be generated from a quantity of fuel when burned or ignited. Anyone who has lit a campfire knows that oak logs will burn (much) hotter than pine logs of the same size. It`s the same principle. Alcohol is also much more temperature-sensitive (temperamental) to colder ambient temperatures than gasoline and its BTU abilities drop off faster than gasoline. So if you notice that your gas mileage seems to be (much) less in cold weather, it`s not your imagination. Idling does not help because you are burning fuel while going nowhere, means zero (0) miles per gallon.
Some drivers switch over non-alcohol gas in cold weather, just for this reason, typically premium-grade gasoline. Will you get better gas mileage?? Depends on the vehicle (truck/SUV versus small car), driving distances, (short commute versus long road trip). and driving style (drag-race starts versus "granny" driving).
You will also have to do the math and check your vehicle`s gas mileage. Premium is usually $0.75 to $1.00 higher in price than low-grade 87 octane blended gasoline. So , for the sake of math simplicity, a gallon of premium fuel at $2.75 per gallon versus a gallon of regular at $2.00 per gallon is 37.5% higher in cost difference (the formula is old-new/old or ($2.00-$2.75)/$2.00 or 0.75/2= .375 or 37.5%). This means that a vehicle that gets 20 MPG in the winter on regular gas would have to get 27.5 MPG on premium to justify the cost difference. Chances are this AIN`T gonna happen. If you get 2 to 3 MPG better, you are doing well. Now, for those who burn E85 (IE; 85% alcohol blend) in their flex fuel vehicles, chances are their fuel mileage is even worse in extreme cold weather. Changing over regular gas (IE 10% alcohol 90% gasoline) may make a larger difference in fuel mileage during cold weather, but again, you would need to do the math to justify the cost increase of regular gas over E85 and check you vehicle`s gas mileage on regular fuel.
As far as starting engines in cold weather, gasoline has a lower volatile temperature than alcohol, meaning gas will turn into fumes at a lower temperature than alcohol, making it easier to ignite (burn) for starting. This factor alone may over-shadow the cost difference and price justification of premium versus regular, especially if your vehicle sits outside in extreme sub-zero F weather and you want it to start easier, like those of you who work a night shift and your vehicle sits outside at work. It`s also the same reason some of us use synthetic oil in engines and do not justify the (much higher) cost of it over conventional oil. You just want the peace-of-mind that your engine is more likely (and easier) to start in extreme cold weather.
