Auto Talk

Winter warm-up

It's a winter morning ritual for many Coloradans: starting up a vehicle and letting it idle for five or 10 minutes to "warm up the engine" while the driver clears snow from the windows, or even leaves the vehicle to do other things. Most of those drivers are unaware that this practice is not only unnecessary, but can actually damage a modern car.

Unless your car was built before computer-driven systems became common (around the mid-1980s), it shouldn't be warmed up at all. Idling, especially in cold weather, causes partially combusted fuel residue to build up inside the engine. Over time, this buildup damages the car's cylinders and many other components, and also makes the vehicle less fuel-efficient.

Although it takes longer in cold weather for a modern vehicle's systems to reach optimal efficiency, this will happen naturally when driving. Idling the vehicle first does nothing to speed up the rate. "It's more than just the engine," explains Gary Sugihara of AAA Colorado's Approved Auto Repair program. "Wheel bearings, transmission, steering, suspension, fluids and tires take time to adapt on a cold morning, too. This can only happen when the vehicle is being driven."

Prolonged idling also wastes fuel, increases air pollution, makes an unattended vehicle vulnerable to theft and can even earn you a ticket in some places. Ten seconds of idling use more fuel than restarting the engine, and just 10 minutes of idling per day adds up to an average of 22 gallons of gasoline a year-at current prices, that's $64 spent on gas that will be simply pumped through a stationary car's engine, out of the exhaust pipe and into the air for no reason.

Worse, the emissions are at a higher level than your car produces when being driven. "The catalytic converter doesn't do its job of controlling emissions until the car has been driven long enough to heat it to operating temperature," says Greg Jozwik, also with the AAA Approved Auto Repair program. "When you idle a cold car, those emissions are passing through the exhaust untreated." Many cities have passed anti-idling ordinances in an effort to lower unnecessary vehicle emissions—Denver, Aspen and Colorado Springs among them.

This winter, make it a goal to remember not to idle your vehicle in the morning for longer than one minute—and that's if the temperature is close to zero or below. In any other case, 30 seconds should be the maximum for a modern car.