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-   -   Winter Fuel Econcomy (http://www.focusfanatics.com/forum/showthread.php?t=303558)

GoShockers 12-03-2012 02:06 AM

Winter Fuel Econcomy
 
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?

BetaDnB 12-03-2012 06:54 AM

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.

skiboarder119 12-03-2012 08:09 AM

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.

JayDeZ 12-03-2012 08:39 AM

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.

SydneyRoo 12-03-2012 09:23 AM

My fuel economy has gone up by 2 mpg ever since I took my summer 18s off and put my winter 16s on. Man those 18s kill my fuel mileage..

ransil 12-03-2012 09:41 AM

Quote:

Originally Posted by SydneyRoo (Post 4481328)
My fuel economy has gone up by 2 mpg ever since I took my summer 18s off and put my winter 16s on. Man those 18s kill my fuel mileage..

Are the tire rotations per mile the same for both sets of tires? Could be a calculation issue.

Sent from my Galaxy Nexus using FF Mobile

SydneyRoo 12-03-2012 09:57 AM

Quote:

Originally Posted by ransil (Post 4481345)
Are the tire rotations per mile the same for both sets of tires? Could be a calculation issue.

Sent from my Galaxy Nexus using FF Mobile

I've checked it out, the rotations ratio is negligibly close. Factory 18s are 235/45/18 and my winters are 205/55/16

jdetzel 12-03-2012 10:18 AM

Quote:

Originally Posted by SydneyRoo (Post 4481366)
I've checked it out, the rotations ratio is negligibly close. Factory 18s are 235/45/18 and my winters are 205/55/16

According to here:
http://1010tires.com/tiresizecalcula...?action=submit
There would be about a 6% increase with the smaller tires.

In other words if you traveled 100 miles your odometer would actually show 106 miles.

It actually says 5.833%, which @ 30mpg would show as a 1.7mpg increase.

That is just what that site says, I do not actually know how to do any of the tire size calculations.

PDQEagle 12-03-2012 12:05 PM

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

gkirk 12-03-2012 12:58 PM

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.


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