February 12, 2010

News & Features

Warm-car wars: Preheating your engine in cold weather is still a subject of debate

The Associated Press

Car warm

(Associated Press)

There are three things you don't discuss over the dinner table: Religion, politics, and how long a car should warm up before driving in the cold.

In December, General Motors issued a news release recommending that motorists warm their engines before driving as a way to reduce engine pollutants.

"While this may seem counterintuitive, a warm engine emits significantly fewer unburned hydrocarbons during the first accelerations," GM said in the release promoting its remote starters for cars, SUVs and pickups.

Warm-car fact
  • A car driven in 14-degree weather for 12 minutes will reach the same operating temperature as one that idles for 30 minutes, according to a study by the Ontario Ministry of Transportation.

"That's because the catalyst that traps the unburned hydrocarbons only activates once the engine is warm," the automaker notes.

Not everyone agrees that letting a car idle in the driveway is a good practice, even on a cold day. Idling will not help emission-control systems reach operating temperatures, according to the Environmental Protection Agency.

"Modern vehicles need little warm-up. Idling for long periods in cold weather can actually cause excessive engine wear," the EPA notes in a report.

And idling is a source of pollution that governments are looking to reduce because of airborne particulates and smog, says Jennifer Feyerherm, director of the Sierra Club's Wisconsin Clean Energy Campaign.

"Cars run more efficiently when they are being driven rather than idling," Feyerherm says.
Technically, you can get in your vehicle and drive without a warm-up even on the coldest day. The electronic fuel systems and lubricants in newer cars can handle low temperatures, says Ken Kempfer, an automotive technology instructor at Fox Valley Technical College in Appleton, Wis.

A car will warm up quicker when it's driven, says Joe Bruzek, an editor at Cars.com, a Web site for car enthusiasts. Drive gently the first few minutes in the cold, but a minute or two is enough of a warm-up, according to Bruzek.

"Letting your car idle in the driveway for 10 minutes is more about getting into a warm, toasty vehicle after drinking your coffee in the living room," he says.

Car warm jump

Technically, you can drive without a warm-up even on the coldest day.

There are merits to running your car's engine some before driving in the bitter cold -- especially if it helps clear frost off the windows.

"I would want to warm up my car a little bit before I put my baby in it," Feyerherm says.
A car's lubricants and fluids are sluggish in the cold, says Gary Klopp, director of automotive services for AAA-Minnesota.

"Let the car come to its senses, so to speak, before you put it in gear," he says. "That's going to be much better on most of the mechanical components."

Klopp says he can tell by the sound of his car when it's ready to go. He has learned to listen to the creaks, groans and other noises associated with a cold engine and transmission.

"When you start your car in extremely cold weather, there's high oil pressure, friction and other things going on. Everything in the engine is trying to find its mechanical mate and jive," Klopp says. "To just start the engine and take off, I think, is abusing the car. At some point it's going to result in premature wear."

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