Mileage Drop - Winter Blend Fuel Time

[Dirtman]

I'm not a scientist... that's just my understanding on how it works. If the gas doesn't completely vaporize in the combustion chamber you get more unburnt fuel going through the exhaust. Winter fuel is designed to vaporize better to burn completely in cold weather and those additives they use to make it do that somehow lower it's energy.

Your right about physically using more fuel in the cold, dense air means more fuel to reach 14.7:1 fuel air mix. The maf/map tell the computer the temp, flow and density of the incoming air. The computer says "you need this much fuel for a perfect mix" then the o2 sensor says "hey computer, your an idiot there's still unburnt fuel down here" and the computer adjusts again and leans out the mix.

But if it did that with summer fuel thats not burning right in -20 degree weather it would end up making the engine run too lean and possibly damage it.

Again not a scientist, no idea on specifics... that's just how I understand the principles of the winter vs summer fuel nonsense.

 

[8thTon]

They add more butane to the mix. Originally that was to increase the vapor pressure to make it easier to start carbureted engines in cold temps, but these days it’s mostly because it’s cheaper - so they let them do it in the colder seasons when evaporated pollution isn’t such an issue.

Unfortunately it also has less energy, or at least transfers less, so once the computer adjusts the mixture you end up using more. Just like E10 and oxygenated fuels.

 

[Dirtman]

I'd tend to agree with @8thTon or literally anyone else with a better theory lol. My knowledge comes from years of drinking.

 

[Bill]

8thTon is correct. Winter blends have less energy, so more fuel is needed to net an equivalent output as the summer blend. The same concept applies to other alternative fuels. They aren't as power dense as gasoline, so more of natural gas, propane, or alcohol is needed.

I haven't noticed a detectable difference when blends are changed, but my driving type is all over the place (highway, city, 80mph on one trip, 65 on the next, etc), so its really hard to get a good figure on a change of a .5 mpg, or whatever it is. I think temperatures have a much bigger impact on fuel economy than the winter blend. I'll tell you this much, the Duratec hates winter. I can get 28-29 mpg driving during the hot summer afternoons. Around 26 on the highway during the winter. 24 mpg around town in the summer, down to 20-22 in the winter. And this is in a winter climate with lows in the 30s and 40s, highs in the low to mid 50s most of the time. It's not really cold here compared to other parts of the country. Mid-20s is usually as cold as it gets most years.

 

[Bgunner]

In my Google searching for the differences between Summer and Winter mix I was surprised to find that there are ( as of 2017) at least 14 unique types of summer-grade fuel sold nationwide. No wonder manufactures have issues with getting better fuel economy when the fuel vary's so widely. Source: https://www.caranddriver.com/news/a15339380/the-vapor-rub-summer-versus-winter-gasoline-explained/ . Although this article covers more of the summer mix than the winter and doesn't touch much on the mix so the search is still ongoing for winter mix answers.

ON a general comparison I have found this info on the differences:

A typical summer-grade gasoline is composed of fluid catalytic cracker gasoline, 40%; straight-run gasoline (directly from crude oil distillation), 25%; alkylate, 15%; reformate, 18%; and butane, 2%. Winter-grade gasoline usually contains more butane, which has an octane rating slightly below premium gasoline (91-93 octane). While butane is an economic component of gasoline, the high volatility of butane limits the amount of butane that can be used in summer-grade gasoline.
Source: https://www.eia.gov/todayinenergy/detail.php?id=11031

I'd tend to agree with @8thTon or literally anyone else with a better theory lol. My knowledge comes from years of drinking.

As I sit here researching with a beer next to me...

 

[8thTon]

As I sit here researching with a beer next to me...

Well hell yeah, how else can a man concentrate?