Anyone know whether there are specific patterns for when winter gas is distributed in what region? I'm in Arkansas, where we got our first frost about Halloween. I am definitely NOT one of the mileage stars on this bulletin board (46.3 real mpg over about 18,500 miles; about 48 mpg or so in the summer). On the last couple of tanks, I seem to see a drop off in mileage, back to the mid-ish 40s. By the way, does anyone know if the timing of winter gas distribution is driven by EPA regulations, or if the companies have their own patterns. If it's free enterprise, does anyone know if there is much variation between companies? And if there is, what's the smartest thing to do about it to minimize overall pollution? Thanks.
I'm in NJ and I've also recently noticed a slight drop in MPG's. Since June I've averaged about 50.5 MPG and over the last month or so it's been dropping to around 48-49 per tank, identical commute. I thought it might be the cooler weather but maybe the gas? Anyway it's still amazing gas mileage!
I don't think 10% ethanol has anything to do with winter fuel. We have 10% ethanol year round in South Florida too. From what I understand, in the winter the fuel formula is slightly different wherever it is required.
Kgall, we got our winter formulation in mid October. That's a fairly typical date for us. Joe166, you are correct. Winter formulation has nothing to do with Ethanol. Winter formulation has a different balance of additives to help keep smog down during the colder temperatures. This formulation change happens whether the gas has Ethanol in it or not.
So, with the winter forumula in gas even without Ethanol you are going to take have a decrease in MPG. So with winterized gas with 10% Ethanol added besides, is it safe to assume that you will even take a bigger hit in MPG's? al
Mark57-- Thanks! How can you tell you got the winter formulation? Actually, the real question is: how can the REST of us tell when we get the winter formulation? Ken
Al, It is my understanding from the chemical engineers on this website that ethanol is less "energy dense" than other chemicals which make up gasoline. So, a gallon of pure ethanol would have less chemical energy than a gallon of pure gasoline. So, year round, you might get fewer MPGs than someone using pure gasoline under the same conditions and driving style. (I don't pretend to know whether ethanol is overall more efficient than gasoline.) But the extra hit you take in winter is what comes from the winter gas formulation. NOW GANG, AM I RIGHT ABOUT THIS? Winter gas burns more efficiently in the winter than summer gas would. I.e., it gets a higher percent of the energy available from its formulation. That's why it produces less smog.
The winter formula will give you a lower MPG with or without Ethanol. You raise an interesting question. Which blend does the winter formula hurt more, 100% or with Ethanol? Good question. I'm sticking with 100% gas as long as I can find it. I see an immediate mpg drop when the winter formula hits. It's not as pronounced in my Prius because my mpg's are down due to cooler weather anyway. It used to make a huge difference in my 4Runner. I'd go from 20 mpg in town to 17 mpg. Conversely, you can see the same change the other way when it goes away in the spring. The winter formula is sometimes called winter oxygenated gas. The oxygen helps the engine to burn cleaner which reduces carbon monoxide. Cold engines are pretty dirty until the warm up and spew a lot of carbon monoxide until they're hot. This winter gas helps that.
Prior to oxygenated fuels and other smog prevention measures, winter gas had a higher vapor pressure to allow easier cold starts. Summer vapor pressures were lower to prevent vapor lock. The summer blend was more dense, having higher energy density by volume. This was sometimes a problem when the delivery trucks were not warned of the changeover, causing some of them to exceed legal load limits at the nearby truck weigh station. At one time in history, a delivery error caused a string of dead cars for miles down the road from a newly restocked station, all with vapor lock. My chemical engineering contacts at the refinery have long since moved up the management chain, which disconnects them from modern fuel blending rules.
By the way, what does it mean to say that winter fuel is "oxygenated"? That O2 molecules are dissolved in it? That some of the hydrocarbons have O atoms stuck into them? Something else?
^^ Ethanol, the compound, contains an oxygen atom, supposedly leading to cleaner burning. "Oxygenated" refers to a more broad list of oxygen-carrying compounds that were once added to gasoline to perform the same function, some of which are no longer used.
