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Winter Fuel Econcomy

3K views 14 replies 12 participants last post by  Pinion Dominion 
#1 ·
I noticed my average fuel economy dropped around 2 MPG's soon after November. I only fill up with non-ethanol fuel and was wondering if non-ethanol stations use a less efficient "winter blend" similar to normal, ethanol stations.

Also, how much of an impact on fuel mileage does cold air cause? Let's take away the fuel aspect and perhaps even the warm-up period. Does the colder, denser, "heavier" air cause enough problems aerodynamically to make a difference?
 
#2 ·
Colder air is more dense (as you stated) which requires more fuel for proper ignition. It also makes it more difficult for the car to cut through the air (aerodynamics). 2 mpg isn't bad of a drop. I lose about 5 mpg in winter also only using ethanol free.
 
#3 ·
Whats said above is true, although with more dense air and more fuel to me would just mean that much more horsepower, so I always figured it was negligible (just my own deduction, I have no facts on that). Coming from a gearbox design background the thing that always gave us the most trouble was any type of bearing or coupled joint. In lower temperatures, they just never seem to warm up enough to have the same efficiency. I've always assumed wheel bearings and CV joints accounted for most of our winter losses.
 
#4 ·
Here in CT they change the gas blend in November. The winter blend is less expensive (or so they say) than the summer bled, but it drops gas mileage by about 2-3 MPG. I went from 33 MPG average over the summer to 29-30 MPG now.

Check around to see if your state changes the gas blend for winter. That might be the problem.
 
#9 ·
I've gone thru 7 winters in massachusetts, and drive the same commute each day, with little weekend travel. My commute is not highway, but I can go 45-50 most of the time, with few stops and slowdowns. Summer I get a consistant 30-31 mpg, winter consistant 27-28, like clockwork.
The cold effects in several ways. All fluids (oil and grease) are thicker so offer resistance. Tire pressure goes down, if you haven't checked it. My previous Eclipse with awd, in summer backing up out of the drive, clutch in, it would coast. In winter, definitely stop coasting much quicker.
Gas gets vaporized poorer so less efficient burn (regardless of electronics), engine warm up even if you start off rightaway, traffic slowdowns.
The change from summer to winter gas is mostly to ease vaporization, and I can't believe the little power difference would make much difference
 
#10 ·
Don't forget that tire pressure will drop a bit with temperature too. Not sure exactly how much it will drop, but I found a reference that it is about 1psi / 10 degrees F.

So if you inflated them at 70F, they will be 3-4 psi lower at 32F. That can cause a noticeable drop to gas mileage.
 
#12 ·
Also, how much of an impact on fuel mileage does cold air cause? Let's take away the fuel aspect and perhaps even the warm-up period. Does the colder, denser, "heavier" air cause enough problems aerodynamically to make a difference?
To produce an identical level of aerodynamic form drag, if the air density is increased then the velocity must correspondingly decrease.

In highly idealized situation if the air pressure happens to be the same at two different temperatures, then the new velocity is simply the original velocity times the square root of the new temperature divided by the square root of the original temperature. (Use absolute temperatures in the calculation)

For instance, if a vehicle is traveling 70 mph at 70F, then it experiences the same amount of form drag at 67.3 mph at 30F.
 
#15 ·
Today I drove my usual 4.1km to work. The temperature outside was -19 degrees Celsius.

When I started my car the distance to empty was 401km. When I got to work the distance to empty was 380km! (When I fill up to max, distance to empty is 540km)

Now I always found the distance to empty was a pretty accurate number as it seemed to be tailored for city driving. For example, when I drive 120km (90% highway) to visit family, the distance to empty goes down at max 80km.

Is there any tips you guys have to improve winter fuel economy?
 
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