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?
