Winter gas vs summer gas

[NevadaGeo]

As every winter, I have noticed a marked decrease in mpg now that winter gas blend is at the pumps. When brand new and with mostly interstate driving this last summer, The expy was getting over 20 mpg with 91+ oct. gas. Now, mostly with the same driving conditions, I have been getting low 18s mpg. I have read that winter gas is blended with butane to give the gas a higher vapor pressure for quicker cold winter ignition. Apparently, the butane additive gives a net 1.7% decrease in energy, accounting for the drop in mpg. I haven't done much research on this, but has anyone seen a like drop in mpg from about mid-September to current?

 

[DieselMonk]

Summer driving will always have better fuel economy. While we do switch between winter and summer fuels, remember that the engine needs more fuel during cold days just to keep running.
I swear that the old 6.0L GM V8 got about 10 - 11 MPG empty in the winter with stock tires and it had a 39.5gal tank and had nowhere near the power than the Expi has now.
Now with my high output limited stealth performance and 3.73 rears I get about 17 mpg with proper winter tires mounted and 21mpg if I stay out of the gas pedal and go for a 500mi ride on the highway. I think high octane gas is good for the engine in the summer specifically when it’s hot and you give her the berries, in the winter there is no benefit at least to me not since the temps are below 32F and I don’t tow any trailer either.

 

[2018ExpyPlatinum]

Not sure your decrease in mpg is butane related. When I used to haul fuel, one certain supplier used butane all year long. The decrease is the winter blend, and the cold weather.

 

[NevadaGeo]

Winter cold makes sense in having poorer fuel economy. Any liquid has a lower volatility as its temperature decreases. I just read that most refiners blend winter gas with butane to increase the volatility for faster cold temperatures ignition.

 

[BigOleFordFan]

This reminds of an old friend from way back that suggested we put a few gallons of Wild Turkey 101 in our tanks every 500 miles or so in the winter, claiming that it would "solve all our MPG problems".....

Fortunately I was smart enough not to listen to him

Note that this was back when we still had "Regular" gas available and unleaded was considered an unnecessary & pricey luxury for most vehicles...

 

[Fizzy]

The offset to this is that colder air, is denser air, which results in better engine performance.

Honestly, you're driving a cruise ship on wheels. If you're that worried about a couple percentage points in fuel economy, you should probably buy something more efficient.

 

[LazSlate]

As an avid 2 stroke enduro rider using carbureted bikes. Altitude and Ambient Temp affect performance. High Altitude the air is less dense so the engine needs less fuel which equates to less power (turbos compensate for this some what and the computer leans out fuel mixture). My bikes I have to re-jet. Ambient temp is the second factor. Cooler air is more dense requiring more fuel to balance out. So your mixture is richer in the winter thus more fuel burn. No way around this without pre-heating the intake air. Gas types have very little effect on the fuel consumption.