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This is why people still think they should idle their cars in winter

Astrid Riecken for The Washington Post.

My article last week, "The biggest winter energy myth: That you need to idle your car before driving," has triggered an overwhelming response. Reading through reader e-mails, I'm struck by one thing in particular: There is a vast gap between what the U.S. government advises and what many people think you should do.

My story, which focused on the fuel and energy consequences of idling, drew on statements by the Environmental Protection Agency and Department of Energy, both of which are negative on the practice. Here’s the Department of Energy:

Avoid idling. Think about it -- idling gets you 0 miles per gallon. The best way to warm up a vehicle is to drive it. No more than 30 seconds of idling on winter days is needed. Anything more simply wastes fuel and increases emissions.

And here’s the EPA’s Office of Transportation and Ambient Air Quality, which takes, if anything, an even harder line:

When a car idles for more than 30 seconds, it has several negative effects, such as increasing air pollution unnecessarily, wasting fuel and money, and causing excessive wear or even damaging a car’s engine components, including cylinders, spark plugs, and the exhaust system. Contrary to popular belief, idling isn't an effective way to warm up most car engines. Today's automobile manufacturers recommend driving off right away and urge that drivers wait no more than 30 seconds to begin driving, even on the coldest days.

So it's quite clear that from an energy and fuel perspective, these authorities think idling makes no sense. And that's also the feeling of many state and local governments on the matter (for instance, see here). But what do readers think? Many thought idling does make a lot of sense. Here are some of their top arguments, and my responses.

1. Idling for safety and comfort. Perhaps the greatest volume of responses came from people saying they could care less about energy concerns -- they idle their cars not for engine reasons, but to help defrost them and remove ice so that they can drive safely. That's not the focus of government agencies in this regard, but it is clearly a highly defensible use of idling.

I'd also add that if agencies want to get people to idle less, they may need to more to directly address their comfort and safety concerns. Because a message that's solely about energy savings may be missing the target.

2. But what about the oil? A large number of readers worried that in cold weather, engine oil has to be heated up before driving. In other words, they suggested that they idle not for the engine, but for its oil in particular.

The right response, on this front, seems to be that people should be making sure their vehicle has the right oil in it for winter driving. Or as the American Petroleum Institute, which licenses and certifies engine oils, puts it, "Operators should refer to their owner's manuals to select the proper viscosity oil for the ambient temperature and operating conditions at which the equipment will be used."

As API notes, multigrade oils today are capable of working both at very cold temperatures and also warmer conditions. Mobil 1 synthetic motor oil, for instance, “flows at temperatures as low as -40 degrees Fahrenheit,” notes the manufacturer, “so that your car gets the oil it needs immediately at startup.”

This raises a larger point -- your particular idling practices may depend on your car, its make and age, and where you live. So you should consult your vehicle manual to see what it says about idling (if anything), and about preparing your car for winter driving. And you should also consult your dealer or mechanic for advice that is particular to your own vehicle or situation.

3. But what about super cold weather? It is extremely cold in much of the U.S. right now, and many of the reactions that I received were about driving in such extreme cold temperatures. That includes this Alaska Dispatch News article, quoting several Alaska auto shop owners who agree that cars warm up faster when driven, but also defended more lengthy idling in cold extremes (as well as the use of engine block heaters to warm up engines).

The EPA and Department of Energy don't seem to make any temperature-related exception for idling, but some other sources do. NPR’s Car Talk, for instance, was highly critical of idling in a 2008 segment. But as the late Tom Magliozzi put it, “If it's bitterly cold out, like 10 or 20 degrees Fahrenheit or lower, you can let it warm up for a minute or two to allow the oil to thin out a bit and circulate completely. But other than that, if it runs, driving it gently is the best way to warm it up.” (Car Talk's emphasis on driving gently to warm the vehicle up -- not flooring it -- is definitely worth bearing in mind.)

Similarly, the City of Minneapolis cites the DOE in recommending only idling for 30 seconds in winter, but it also makes an exception for days that are super cold. In general, while Minneapolis limits idling to 3 minutes, there’s a cold weather exception: “Vehicles may idle up to 15 minutes in a one hour period if the outside air temperature is less than zero degrees or higher than 90 degrees.”

Finally, Natural Resources Canada, like the U.S. agencies, considers the need for idling to be a "myth," and similarly stresses that "the best way to warm [your car] up is to drive it." However, Natural Resources Canada gives a longer idling window in winter than the U.S. agencies' 30 seconds, writing, “In fact, with today's computer-controlled engines, even on cold winter days, usually no more than two to three minutes of idling is enough warm-up time needed for the average vehicle before starting to drive – but make sure that windows are free from snow and properly defrosted before driving away!”

From this, we can conclude that while the U.S. government's experts consider 30 seconds to be a good general rule for cold weather idling, numerous sources do see exceptions for extreme cold weather. Or at minimum, the experts seem rather split on this. As usual, safety is paramount, and drivers should consult their vehicle manual, dealer, and mechanics for more info.

Nonetheless, it's clear that we're wasting a lot of energy on unnecessary idling. All of that said, the fact remains that in comparing expert agencies' recommendations on cold weather idling (30 seconds for U.S. agencies, up to a few minutes for Natural Resources Canada) with the amount of idling that people say in surveys that they think is necessary when the temperature is below 32 degrees (5 minutes!) there’s a huge gap. So there’s a lot of energy waste happening here.

By being more thoughtful about idling, we should definitely be able to save money and energy alike -- while helping out our cars and staying safe to boot.