Is "Winter Gas" a scam?

[dl1027]

My gas mileage drops every winter about 2 or 3 mpg. That's at least a 10% drop. This got me to thinking about the reasoning behind "winter gas", that is, oxygenated gasoline.

Here's what I found on a government website:

How will oxygenated fuel affect vehicle performance?
Because the addition of oxygenates to gasoline increases the octane rating of gasoline, vehicle performance will generally increase somewhat. Because the performance increases, gas mileage may drop but usually only by less than two percent. Cold temperatures and wintertime driving conditions tend to lower gas mileage by more than this amount.

If the performance increases why does the mileage drop?

How does any of this help the environment when it takes the same amount of energy to go from point A to point B? In other words, if the gas formulation causes the engine to be less powerful then more of it will need to be burned to go the same distance. Any gain in emmisions would be nullified by the necessity of pushing that much harder on the gas pedal.

Am I making any sense?

[spithead051]

You are making some sense. What I've been told about winter gas is that it burns easier, making it easier for cold engines to start and warm up. It's better for the engine when the block is 30 degrees to have, essentially, thinner gas.

From what I have experienced I have never had an increase in performance, just a decrease in mileage.

[TrailDust]

The answer is kind of long and complicated, but I'll try to explain in brief. BTW, my best friend worked for over ten years as the lead chemist at a refinery in Los Angeles and gave me lots of insight into the refining industry.

Gasoline as produced in a refinery is made of many different hydrocarbons. The chemists at the refinery who produce that gas need to make sure it has the proper octane, RVP (which is Reid vapor pressure), detergents, etc. Octane may be constant in gas that's produced, but the RVP needs to be adjusted in the colder winter weather.

RVP is the vapor pressure of the gasoline blend when the temperature is 100 degrees and at normal atmospheric pressure, but it averages about 14.7 PSI. Summer gas needs to be adjusted so that RVP is significantly below 14.7 PSI in order to prevent boil-off building up the pressure in your gas tank which is a contributor to air pollution. The EPA mandates summer blends cannot exceed between 7.8 and 9.0 PSI, depending on geographic location. Summer blends contain several different components that all must be assessed for their RVP, with butane being the one component that has the highest vapor pressure around 55 PSI if memory serves.

Butane and all the other components in gas end up contributing to the overall RVP. However, because of butane's high vapor pressure it contributes significantly to the RVP, and so summer blends have a butane fraction that is very low compared to winter gas.

When you add up all these factors the end result is that summer blend gas has more energy per unit volume than winter blend does (by about 2% or so if memory serves), and that's why mileage is better with summer blends. Personally, I think the mileage difference is 5% to 10% depending on a variety of factors, but that's only my personal observation and I have no scientific data to back up that claim.

[05Moose]

I see TrailDust gave us the refinery reasoning. I wonder if there's a better solution out there.

I do know it was pushed by industry to sell their product same as MTBE was (look where that got us when the truth couldn't be hidden anymore). Industry knew MTBE was bad before paying lobbyists in Washington to force it on the consumers (again, proven fact). When Ethanol was out for a half decade or so after MTBE was pulled, there were numerous independent studies around the world (Stanford here in Calif, Australia, on and on...) that showed it actually increased a type of smog in cities that was very harmful to human lungs. Glad I don't live in the valley.

What will really get your goat is when you do the calculations to see how much more you spend for ethanol. While the price is the same as gas, that 2 mpg drop causing you to purchase 2 extra gallons of fuel for every 20 gallons you buy. 20 gallons x 20 mpg = 400 miles compared to 20 gallons x 18 mpg = 360 miles. So for every 20 gallons, you're traveling 40 miles less. What's it take to go those 40 miles? Let's assume you're getting 20 mpg, then that's an extra 2 gallons you're having to buy. At $3.50/gallon, you're spending an extra $7 for every full tank of gas (or roughly every 400 miles). But now I wonder if the explanation given by TrailDust means we'd still lose that even without ethanol in the winter?

So ethanol may add cost to the consumer, causes us to increase our oil imports/use, and harms our lungs. Even the gasoline industry doesn't like it (you'll find studies/comments from companies like Chevron that are against it if you search enough).

Ah, yes. Everybody chipping in their own 2% and nobody really putting it all together (literally). In fact, most of these reasons are all correct, and the big reason why the mileage decrease is more than anyone comes up with using their part, is that all of these parts add together.

So in the winter, you get a higher amount of butane in the gas, for a 2% drop in fuel mileage. You have ethyl alcohol (in many places, this is still seasonal) for a 2% drop, oxygenated cruft for another 2% drop, we're sitting now at 6%.... Then on top of that your motor oil turns as thick as gear oil, gear oil as thick as grease, and grease is like a frozen horse sh*t.

BTW: 10%? Bah! Its bigger than that. I'd say more like 20% -- at least in cold places.

[dl1027]

Originally Posted by TrailDust

RVP is the vapor pressure of the gasoline blend when the temperature is 100 degrees and at normal atmospheric pressure, but it averages about 14.7 PSI. Summer gas needs to be adjusted so that RVP is significantly below 14.7 PSI in order to prevent boil-off building up the pressure in your gas tank which is a contributor to air pollution. The EPA mandates summer blends cannot exceed between 7.8 and 9.0 PSI, depending on geographic location. Summer blends contain several different components that all must be assessed for their RVP, with butane being the one component that has the highest vapor pressure around 55 PSI if memory serves.

Butane and all the other components in gas end up contributing to the overall RVP. However, because of butane's high vapor pressure it contributes significantly to the RVP, and so summer blends have a butane fraction that is very low compared to winter gas.

If I'm understanding this, you are saying that winter gas is the normal blend and summer gas is adjusted to reduce gas fumes in the air? Why can't we then have summer gas year round? Why isn't winter gas any cheaper?

[dl1027]

Originally Posted by 05Moose

When Ethanol was out for a half decade or so after MTBE was pulled, there were numerous independent studies around the world (Stanford here in Calif, Australia, on and on...) that showed it actually increased a type of smog in cities that was very harmful to human lungs. Glad I don't live in the valley.

Yeah, we're choking down here in the valley. But it's not the MTBE. It's all the people burning wood in their fireplaces. I guess people would rather have a log on the fire than breath.

[TrailDust]

Originally Posted by 05Moose

I do know it was pushed by industry to sell their product same as MTBE was (look where that got us when the truth couldn't be hidden anymore). Industry knew MTBE was bad before paying lobbyists in Washington to force it on the consumers (again, proven fact).

Funny thing is, my best friend oversaw the introduction of MTBE at all refineries in the L.A. area, and just a few years ago my brother-in-law who works for a remediation company oversaw the removal of MTBE at all the same refineries. What are the chances, huh?

Originally Posted by mr.reaper

BTW: 10%? Bah! Its bigger than that. I'd say more like 20% -- at least in cold places.

With ethanol my own estimate is a 10% hit on mileage. I often drive to Nevada where there in no ethanol in the gas, and every damn time the mileage difference is 10%. At least that's for my area, my region. Like you suggested, it wouldn't surprise me at all if people see more or less MPGs in their local area due to any number of factors.

Originally Posted by dl1027

If I'm understanding this, you are saying that winter gas is the normal blend and summer gas is adjusted to reduce gas fumes in the air? Why can't we then have summer gas year round? Why isn't winter gas any cheaper?

Even winter gas is adjusted for RVP, but the relative amount in comparison to summer gas in nowhere near as much. As far as price, summer gas is always more expensive to produce than winter gas, but other factors in the marketplace, such as supply-and-demand, crude oil price, refinery shutdowns, etc., affect the price at any given time. Anyway, summer blend is more expensive for the refineries to produce, that's the bottom line.

Originally Posted by TrailDust

With ethanol my own estimate is a 10% hit on mileage. I often drive to Nevada where there in no ethanol in the gas, and every damn time the mileage difference is 10%. At least that's for my area, my region. Like you suggested, it wouldn't surprise me at all if people see more or less MPGs in their local area due to any number of factors.

There is not a chance that ethanol by itself can cause a 10% drop in mileage. That would only happen if the ethanol was 100% inert. As I understand it, ethanol releases approximately 90% as much energy as gasoline (obviously depending on the constituency of the gasoline), but taking 90% as the reference, we only see really a 10% of 10% = 1% loss of energy on account of the ethanol by itself. We *may* be able to stretch that up to 2% at the remote end, but no way 10%.

*** which isn't to say that you didn't observe an honest 10% hit... just that there must have been other factors involved than throwing in straight 10% ethanol.

Originally Posted by dl1027

If I'm understanding this, you are saying that winter gas is the normal blend and summer gas is adjusted to reduce gas fumes in the air? Why can't we then have summer gas year round? Why isn't winter gas any cheaper?

I wouldn't say that either is the "normal" blend.
The idea here is that you don't want the gas to evaporate out of the tank too fast.

Remember that RVP is the vapor pressure AT 100 DEGREES. So you take 14.7 at 100 degrees for the summer. In the winter, you can ramp up the RVP to, (I don't know the real number, so this is just an example) say 25 at 100 degrees. Because its colder in the winter, 25 psi at 100 degrees will drop to 14.7 psi at... 40 degrees. Get it?

So basically, they have a TARGET pressure that they adjust to.

You adjust to a lower pressure by selecting heavier molecules... i.e. longer carbon chains, like octane. You adjust to a higher pressure by selecting a lighter molecule -- shorter carbon chains, like butane.

The longer the carbon chain, the more energy the molecule stores. An octane molecule, C8H18, has 25 single bonds. A butane molecule, C5H12, has only 16 single bonds, or 16/25th of the amount of energy.

Now you ask why they don't just keep the summer gas through the winter, so what if the pressure sits at 5 psi at 40 degrees, eh? Well the problem here is that the stuff will be really hard to ignite in a cold engine! So if everybody would be happy to use a fuel system heater and an engine block heater, then no problem, the summer gas will be just fine in the winter. Problem though, is that just isn't going to happen.


As far as the price of winter and summer gas.... well I'm going to have to disagree with you on them being the same price. Its about a 20 cent per liter (roughly 75 cents per gallon) difference here, summer gas does cost more. Nearly 17% -- gas is $1.20/liter right now. It'll go back up to about $1.40 for the summer.

[TrailDust]

Originally Posted by mr.reaper

There is not a chance that ethanol by itself can cause a 10% drop in mileage. That would only happen if the ethanol was 100% inert. As I understand it, ethanol releases approximately 90% as much energy as gasoline (obviously depending on the constituency of the gasoline), but taking 90% as the reference, we only see really a 10% of 10% = 1% loss of energy on account of the ethanol by itself. We *may* be able to stretch that up to 2% at the remote end, but no way 10%.

*** which isn't to say that you didn't observe an honest 10% hit... just that there must have been other factors involved than throwing in straight 10% ethanol.

What you suggest is very possible, but I'm okay with blaming it all on ethanol that state gubments mandate....

[08TRDOFFROAD]

In my opinion, all gas is a scam!