While environmentalists would argue you should never let your engine idle due to the unnecessary greenhouse gas emissions, such an edict may run thin in sub-zero temperatures. In fact, it can be unsafe—let alone uncomfortable—to drive a car without first warming up the engine.
Should You Idle Your Car to Warm It Up?
You should warm up your vehicle if it is carbureted. If your car is fuel-injected, then it is a personal matter of how much you can tolerate the cold. When 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 having time for the oil to heat up, thin out, and lubricate the engine. Newer cars that use fuel injection and computer controls are good to go without idling.
Does Running a Car Heater Use Gas?
Running the air conditioner consumes gas, but cranking up the heat does not. Running your car’s heating system is only wasteful when you’re waiting for the car to warm up, because an idling engine consumes gas. If you start your car and let it idle, it will use the exact same amount of gas whether the heat is on or not. Cars always use gas when the engine is running, even while idling. So there is no extra fuel cost with turning the heater on versus simply running the engine. This is due to the fact that heater systems utilize waste heat from the engine. That waste heat is either dissipated or used to warm up the interior of the car.
Is It Necessary to Idle a Car Before Driving It?
In most cases it is not necessary to idle a car before driving it. Older vehicles that lack fuel injection systems are an exception. Depending on your cold tolerance, you may need to idle the car to warm up the interior before a drive. In such cases, a block heater is a more effective way of preventing engine damage than letting an engine idle after sitting in sub-zero temperatures. Although a block heater can warm up the engine, it cannot do anything to warm the interior or defrost the windows.
How Much Does Idling a Car Cost?
The cost of an idling engine depends on a lot of variables. The Argonne National Laboratory performed a study on three different engines, including a 1.8L Honda Civic, a 2.5L Ford Fusion, and a 3.6L Chevrolet Malibu. For each of these engines, idling for 10 minutes consumed the following amounts of fuel:
1.8L Honda Civic: .026 gal2.5L Ford Fusion: .082 gal3.6L Chevrolet Malibu: .14 gal
Paying $2.90/gal for gasoline would mean that idling your car for ten minutes would cost roughly $0.08 - 0.41, depending on the size of the engine. You can use these numbers and other gasoline prices to estimate the cost of idling for shorter or longer periods. If you have a larger engine, then you have to figure it will cost more. While a quarter here or there is unlikely to break the bank, it’s easy to see how the costs of idling could add up over time, especially when gas prices trend higher. If you drive a vehicle with an engine that’s bigger than 3.6L, and you idle for 10 minutes each day, you could be spending over $50 in gas over the course of the winter.
Is It Cheaper to Use a Space Heater to Warm up a Car?
According to the data from the US Energy Information Administration, the national average price of electricity is $0.13 per Kilowatthour (KWh). That means a 1000W plug-in car heater used to heat up your car and to defrost the windshields will cost roughly 13 cents for an hour of use. Depending on where you live, that amount may be slightly higher or lower. This also means that, unless you’re driving a car that has an engine in the 1-liter range, it’s significantly cheaper to run a space heater for an hour than it is to idle for ten minutes.
