[MetroMPG.com] List of reasons why your winter mileage is so bad

[MetroMPG]

It happens every year. Summer ends, Autumn expires, and your fuel economy plummets.

Something else happens: as northern hemisphere winter sets in, I get tons of hits on the MetroMPG.com article: 9 reasons why your winter fuel economy bites!

It's been linked by literally dozens of other car forums, which I see in the web logs for the site. (This week, it's a discussion at Rav4World: Gas Mileage in Winters).

Here are my original 9 points, in summary.

Can we come up with anything I missed? If so, I'll update the article and make it even more useful for folks.

(Keep in mind this was written for the "average" motorist. I'm sure you ecomodder/hypermilers don't do any of the things that can be avoided...)

1. More idling

2. Low tire pressure
(failure to compensate as temperature drops)

3. Increased rolling resistance
(even at the correct pressure, cold, hard tires don't roll well)

4. Crappy road conditions
(snow, wet and slush adds significant rolling resistance)

5. Lower average engine temperature
(more fuel enrichment)

6. Higher average lubricant viscosity
(not just engine oil, but transmission, differential, bearing grease...)

7. Weaker gasoline
(the dreaded winter gas!)

8. Higher electrical loads
(with less daylight, we run more often with lights, not to mention wipers, defrost, heater blower, seat warmers, etc...)

9. More aerodynamic drag
(drag increases as air temperature drops. There's a reason Bonneville racers like high elevation and hot summer air)

So... what did I miss?

I've since come up with three more things that I didn't originally think of, because I don't own the type vehicle they apply to. But others must experience:

10. Degraded battery performance / more alternator load
This is related, but distinct from #8: One thing driving an EV has taught me is that lead acid batteries are terrible in the cold. Resting voltage is lower, as is capacity. So, in cold weather the alternator has to work harder to restore & maintain battery voltage at level the regulator wants to see.
11. Automatic transmissions in "cold mode" longer (related to #5).
In newer cars, the shift pattern is often modified to cause higher RPM engine operation until the coolant reaches a certain temperature. On some cars I've driven, the torque converter will NOT lock at cruise regardless of speed or load/throttle position until that pre-set temperature is surpassed.

12. Added weight
Owners of RWD vehicles often place significant extra weight (eg. bags of sand or salt) in the back of the vehicle for traction in snow. Also, how about not cleaning heavy ice and snow off? We just had an ice storm that put a thick, heavy coating on everything.


13. More use of 4WD/AWD
Whether engaged by the driver or the computer, driving all four wheels instead of two will burn more fuel.

Do I hear a #14? #15?

[Lazarus]

What about the fact that you have shorter trips because alternate transportation is rough in the winter if you walk, motorcycle, bike etc.

I don't know how you would quantify this but what about all the holiday travel and shopping that goes on from November to Jan.

Also is there really a winter blend anymore? I'm sure some parts of the US have regular gas but is not E10 just about every where now?

[SVOboy]

I would also posit that just driving during the snow, much less snow on the ground, would suck.

Also, does canada use e10 now?

[MetroMPG]

Originally Posted by Lazarus

What about the fact that you have shorter trips because alternate transportation is rough in the winter if you walk, motorcycle, bike etc.

THAT's a good point! Good stuff.

It's absolutely true in my case: I do use the car much more in the winter. Probably haven't put 25 km on the bicycle in the last 3 or 4 weeks. Maybe it doesn't apply as much to the average Joe who drives 4 blocks to get milk all year round, but worth a mention nonetheless.

Not sure about the holiday travel - wouldn't that be balanced out by the summer road trips? I'm sure somewhere you can find out the busiest week on a nation's roads. Something tells me it's in the summer.

[MetroMPG]

Originally Posted by SVOboy

I would also posit that just driving during the snow, much less snow on the ground, would suck.

Also, does canada use e10 now?

E5 average blend became mandatory in Ontario in Jan of this year (07). Does that replace the need for winter formulation?

And yes, driving IN snow is brutal. Especially when it gets churned up and turns to something approximating sand. I saw this in my last drive in the ForkenSwift on snow covered roads. Normally I aim to keep the amps at around 50-70 when accelerating (unmolested by other traffic), but in this snow I couldn't even maintain forward progress at anything less than 90 or 100A.

[Lazarus]

Originally Posted by MetroMPG

Not sure about the holiday travel - wouldn't that be balanced out by the summer road trips? I'm sure somewhere you can find out the busiest week on a nation's roads. Something tells me it's in the summer.

You're probably right although in December most folks are driving around the mall parking lot looking for a space and during the summer they are usually taking longer road trips. I have nothing to back that up just my hunch. I know personaly from November to Jan we take a lot of short trips and more frequent trips then in the summer because of Thanksgiving and all the shopping and Christmas parties and such. Still impossible to quantify I think. It's also a very small chunk of winter for most folks.


Woot for 2 weeks of winter in Central Texas

[Lazarus]

Also is not there something with the fuel density when it cold? I know some pumps are calibrated for temperature. I can't remember if you get more or less with colder temps.

[SVOboy]

More with colder temps. It's not that big of a difference though.

[MetroMPG]

More energy density in cold fuel. But the ECU compensates for it via the o2 sensor - it shouldn't affect consumption. (Unless it's so cold it won't vapourize.)

[RH77]

Another input: (noticed it this morning during Freezing Rain)...

Winter weather often produces more accidents and "slow-downs" -- which tends to clog-up side-streets as well major arteries and highways. The usual free-flow drive could turn into a jam...

Problem is -- this can happen during peak traffic hours or otherwise.

RH77