For decades, the prevailing wisdom has been that you should let your car idle and warm up before you hit the road. While modern fuel injection and emission control systems have reduced the need, this issue remains a contentious one.

While environmentalists argue that you should never let an engine idle for unnecessary greenhouse gas emissions, such a decree can run dry in sub-zero temperatures. In fact, it can be unsafe — not to mention inconvenient — drive without preheating the engine.

Should you park your car to warm it up?

Car stuck in the snow

All-wheel drive and traction tires can help prevent situations like this.
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You must warm up your car if it is carbureted. If your car is fuel injected, it’s a matter of how much cold you can tolerate.

If you have an older car with a carburetor, the engine will run smoother if it has had a chance to warm up. Older vehicles also benefit from the fact that the oil warms up, thins and lubricates the engine. Newer cars that use fuel injection and computer controls are good to idle.

Does the car heater use gas?

car interior vents
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Running air conditioner consumes gas and heating it — no. Your car’s heating system is only wasteful when you’re waiting for the car to warm up because the engine is consuming gas when it’s idling.

If you start your car and let it idle, it will use the same amount of gas whether the heating is on or not. Cars always use gas when the engine is running, even at idle. Thus, when the heater is turned on, no additional fuel costs are required, but simply when the engine is running. This is because the heating systems use waste heat from the engine. This waste heat is either dissipated or used to heat the interior of the vehicle.

Do I need to idle before driving?

In most cases, the vehicle does not need to be idle before driving. Older vehicles that lack fuel injection systems are an exception. Depending on your cold tolerance, you may need to park your car to warm up the interior before driving. In such cases block heater is a more effective way of preventing engine damage than allowing the engine to idle after operating in sub-zero temperatures. Although the block heater can warm up the engine, it cannot do anything to warm the interior or defrost the windows.

How much does it cost to idle a car?

The cost of an engine at idle depends on many variables. The Argonne National Laboratory tested three different engines, including the 1.8L Honda Civic, the 2.5L Ford Fusion and the 3.6L Chevrolet Malibu. For each of these engines, idling for 10 minutes, the following amount of fuel is consumed:

  • Honda Civic 1.8 L: 0.026 gal
  • 2.5L Ford Fusion: 0.082 gallons
  • 3.6 L Chevrolet Malibu: .14 gal

Paying $2.90 per gallon for gas means your car will cost approximately $0.08-$0.41 to idle for ten minutes, depending on engine size. You can use these numbers and other gas prices to estimate the cost of idling for shorter or longer periods. If you have a larger engine, then you must understand that it will cost more.

While a quarter here or there is unlikely to break a bank, it’s easy to see how idle costs can add up over time, especially when gas prices rise. If you drive a car with an engine larger than 3.6L and idle for 10 minutes a day, you can spend over $50 on gas during the winter.

Is it cheaper to use a heater to warm up a car?

According to data U.S. Energy Information Administration, the national average price of electricity is $0.13 per kilowatt-hour (kWh). It means that plug-in car heater power 1000 W used to heat your car and defrost your windshield will cost approximately 13 cents per hour of use. Depending on where you live, this amount may be slightly higher or lower.

It also means that, unless you’re driving a car with an engine in the 1L range, it’s significantly cheaper to run the heater for an hour than it is to idle for ten minutes.

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