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Cold weather = poor mileage

by David Zatz on

The Oak Ridge National Laboratory recently tested cars to show that gas mileage can drop by up to 22% in short-trip driving (3-4 miles) during even mildly cold weather — with hybrids faring even worse, dropping by up to 34%.

The lab looked at 600 conventional vehicles and 14 hybrids under “normal” temperatures (around 77°F) and cold-weather conditions (20°F).

Neon in snow

Culprits include friction from oil and other fluids, the engine running at below-optimal temperatures (when leaner gas/air mixtures kick in), the added power from heated seats, defrosters, and such, higher aerodynamic drag due to denser air, and lower tire pressure which increases rolling resistance. For hybrids, one issue is lower battery performance; either way, the alternator has to work more to keep a charge. Finally, icy or snow covered roads increase wheel slip, and can bring energy-consuming all wheel drive into play.

In addition, many owners still do extended warm-ups, especially now that many cars have remote starters. It is not unusual to find people leaving their cars running in winter, while they run errands indoors.

The DOE and EPA issued some recommendations, which may seem obvious:

  • Park in a warm place, such as a garage (or, we add, in the sun)
  • Combine trips to drive less often with a cold engine
  • Reduce idle warm-up times;  modern cars usually do not require much warming up (this is in the owner’s manual)
  • Shut off seat warmers and defrosters when not needed
  • Check the tire pressure regularly
  • Use the correct oil for cold weather
  • Preheat the cabin of a plug-in hybrid or electric car
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