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The Debunker: Should You "Warm Up" Your Engine on a Cold Day?

by Ken Jennings

December is a month full of festive observances, but one of the most important often gets overlooked: National Impaired Driving Prevention Month! Between all the holiday merrymaking and the terrible road conditions, it's a pretty good time to think more carefully about our driving. But what if not everything you think you know about the rules of the road is accurate? We have Jeopardy!'s Ken Jennings behind the wheel all month to set you straight. Buckle up, check your blind spot, and pull away from the curb when it's safe and legal to do so.

The Debunker: Should You "Warm Up" Your Engine on a Cold Day?

In 2009, a study done at Vanderbilt University found that the average American believes that you should idle a car for more than five minutes on a wintry morning. I'm sure we can all picture some grumpy Midwestern dad heading out first thing to start up his car, and then shoveling the walk or finishing breakfast for fifteen minutes while his engine "warms up."

The Debunker

Unfortunately, this practice should have gone out of style with grumpy Midwestern dads. "Warming up" your car was a good idea back when there was a carbureted engine under the hood. Gas engines are less efficient in cold weather, and old-timey carburetors didn't adjust the amount of gas they were mixing with air to compensate for low temps. So stalls were common on a cold engine. But electronic fuel injection systems started to replace carburetors thirty years ago. Modern engines get no advantage of performance or efficiency from idling any longer than thirty seconds, says the Department of Energy, so you can cut that out this winter. (Unless your car is like thirty years old. In which case I apologize and should probably check my automotive privilege.)

Does it really matter if people sit in a cold car for five extra minutes all winter, as long as they're not late for work? Well, that 2009 Vanderbilt study ran the numbers and estimated that American idling accounted for 93 million metric tons of greenhouse gas emissions each year. That's 1.6 percent of the national total, and twice as much as the entire iron and steel manufacturing industry! It's also not great for your car, say experts. Cold idling means gas is unnecessarily washing away your engine oil, shortening the lifespan of many engine components. And of course you're getting zero miles to the gallon every minute you idle, so starting your car early might make the car interior more comfy, but it's not doing your mileage—or the planet—any favors.

Quick Quiz: What musical duo, which got its start "warming up" Saturday Night Live audiences before the show, went on to star in one of the top-grossing movies for 1980?

Ken Jennings is the author of eleven books, most recently his Junior Genius Guides, Because I Said So!, and Maphead. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at or on Twitter as @KenJennings.