What is the difference between winter and summer gas? What are the refiners eliminating or adding to winter gas to make it give lower mpg? It would seem that they would add something to help winter mpg considering the longer time it takes to warm up an engine. Maybe it's been discussed but I couldn't find the answer.
Summer / Winter gas
- Thread starter Mar57
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I'll add another question ... Why change the blend from summer to winter?
Tons of things go into gas to give it certain properties..
These change with seasons.
an example is Reid Vapor Pressure.
It needs to be correct for the expected temperatures.
https://en.wikipedia.org/wiki/Reid_vapor_pressure
Very generic answer:
Quote:
The matter of vapor pressure is important relating to the function and operation of gasoline-powered, especially carbureted, vehicles. High levels of vaporization are desirable for winter starting and operation and lower levels are desirable in avoiding vapor lock during summer heat. Fuel cannot be pumped when there is vapor in the fuel line (summer) and winter starting will be more difficult when liquid gasoline in the combustion chambers has not vaporized. Thus, oil refineries manipulate the Reid Vapor Pressure seasonally specifically to maintain gasoline engine reliability.
That is one part of the seasonal difference.
These change with seasons.
an example is Reid Vapor Pressure.
It needs to be correct for the expected temperatures.
https://en.wikipedia.org/wiki/Reid_vapor_pressure
Very generic answer:
Quote:
The matter of vapor pressure is important relating to the function and operation of gasoline-powered, especially carbureted, vehicles. High levels of vaporization are desirable for winter starting and operation and lower levels are desirable in avoiding vapor lock during summer heat. Fuel cannot be pumped when there is vapor in the fuel line (summer) and winter starting will be more difficult when liquid gasoline in the combustion chambers has not vaporized. Thus, oil refineries manipulate the Reid Vapor Pressure seasonally specifically to maintain gasoline engine reliability.
That is one part of the seasonal difference.
Originally Posted By: Burt
They can put more butane in winter gas and still meet the reid vapor pressure limit. Butane has less energy content (btu's) per gallon, but more octane.
Originally Posted By: Mar57
I'll add another question ... Why change the blend from summer to winter?
The official line is to raise the vapor pressure so that it evaporates more readily in colder temperatures, thus lowering unburned HC emissions out the tailpipe.
Since that's not even remotely an issue in 90% of the country for fuel injected cars, and it greatly increases the HC emissions out the fuel tank vent system on all cars (especially pre-fuel-injected cars,) I suspect its a convenient way to get rid of lighter, higher vapor-pressure refined fractions at a profit marin that normally happens only for the lower vapor-pressure fuel fractions in the summer.
If it were really about emissions, winter-blend fuel would not exist. My garage REEKS of unburned gasoline when I pull one of the older cars in after a winter drive- you can sometimes hear it gurgling in the tank and fuel lines. One of them will also vapor-lock on an 75-degree winter day when it won't vapor-lock on a 110-degree summer day. Even the 2001 Jeep Cherokee I had would vapor-lock the #3 injector (there's a TSB about it) on a hot winter day on that winter swill. Winter-blend fuel is a re-used waste-product, IMO.
They can put more butane in winter gas and still meet the reid vapor pressure limit. Butane has less energy content (btu's) per gallon, but more octane.
Originally Posted By: Mar57
I'll add another question ... Why change the blend from summer to winter?
The official line is to raise the vapor pressure so that it evaporates more readily in colder temperatures, thus lowering unburned HC emissions out the tailpipe.
Since that's not even remotely an issue in 90% of the country for fuel injected cars, and it greatly increases the HC emissions out the fuel tank vent system on all cars (especially pre-fuel-injected cars,) I suspect its a convenient way to get rid of lighter, higher vapor-pressure refined fractions at a profit marin that normally happens only for the lower vapor-pressure fuel fractions in the summer.
If it were really about emissions, winter-blend fuel would not exist. My garage REEKS of unburned gasoline when I pull one of the older cars in after a winter drive- you can sometimes hear it gurgling in the tank and fuel lines. One of them will also vapor-lock on an 75-degree winter day when it won't vapor-lock on a 110-degree summer day. Even the 2001 Jeep Cherokee I had would vapor-lock the #3 injector (there's a TSB about it) on a hot winter day on that winter swill. Winter-blend fuel is a re-used waste-product, IMO.
Actually, flip that on its head. Emissions requirements are the lower RVP fuels must be used in the summer to minimize emissions from refueling and fuel system emissions. This specifically gets at ozone formation. This is less of an issue in cooler weather, and a big part of why the higher RVP fuels can be used in the winter.
And Carbed applications do notice the difference in RVP - fuel injected - not so much.
It is an acknowledgement that the low RVP fuels cost more to make and a concession that they are not needed year around to address ozone formation.
And Carbed applications do notice the difference in RVP - fuel injected - not so much.
It is an acknowledgement that the low RVP fuels cost more to make and a concession that they are not needed year around to address ozone formation.
Originally Posted By: Mar57
I'll add another question ... Why change the blend from summer to winter?
because winter blend is cheaper to make. Butane is cheaper than natural gasoline. All things equal, winter blends are ~20 cents per gallon less than summer. more than enough to make up for loss in mpg. Environmental considerations aside, I'd rather run winter blend year around.
My guess is winter blend might be better for extreme cold weather starting as well.
I'll add another question ... Why change the blend from summer to winter?
because winter blend is cheaper to make. Butane is cheaper than natural gasoline. All things equal, winter blends are ~20 cents per gallon less than summer. more than enough to make up for loss in mpg. Environmental considerations aside, I'd rather run winter blend year around.
My guess is winter blend might be better for extreme cold weather starting as well.
Due to a poor design, my Jeep won't idle hot without misfiring on cylinder 3 with winter blend gas. It's usually like clockwork. Late October it'll start having issues all the way to spring. Apparently the heat causes the fuel to just evaporate or boil in the injector leading to vapor lock.
I think there is a variety of oxidizers that they can use in the winter. Butane is one. But there are others.
Guys, thanks for the answers to my questions. Now I understand the difference between summer and winter gas.
Originally Posted By: MNgopher
….And Carbed applications do notice the difference in RVP..
It definitely makes a difference in my snowblower. Put some fresh E0 gas in the blower about a month ago, and it started easily at 45F. Fast forward to December, and it would not start at 25F. Drained the E0, put in freshly bought E10, and the blower started easily.
….And Carbed applications do notice the difference in RVP..
It definitely makes a difference in my snowblower. Put some fresh E0 gas in the blower about a month ago, and it started easily at 45F. Fast forward to December, and it would not start at 25F. Drained the E0, put in freshly bought E10, and the blower started easily.
Here in Indiana we have several different gasoline blends throughout the year- 4 levels of RVP just for conventional gasoline
That does not count the RFG gasoline required close to Chicago and Louisville. Here are the different requirements around the country.
(So much for the gas is gas folks
)
US EPA gasoline requirements
That does not count the RFG gasoline required close to Chicago and Louisville. Here are the different requirements around the country.
(So much for the gas is gas folks
US EPA gasoline requirements
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