Why drive a car that gets zero miles to the gallon? Yet that is your mileage whenever your engine idles. Idling a car wastes money and fuel, creates air pollution and generates carbon dioxide that causes global warming.
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Some states even have laws limiting the amount of time cars can idle. Unfortunately, many people believe that idling is necessary or even beneficial - a false perception that has carried over from the 1970s and 1980s, when engines needed time to warm up, especially in colder temperatures (less-than 20 degrees Fahrenheit). Fuel-injection vehicles, which have been the norm since the mid-1980s, can be restarted frequently without engine damage and need no more than 30 seconds to warm up even on winter days.
In fact, idling longer than that could actually damage your engine in the long term. Because an idling engine is not operating at its peak temperature, the fuel does not completely combust, leaving residues in the engine that can contaminate engine oil and make spark plugs dirty. Excessive idling also allows water to condense in the vehicle's exhaust, contributing to corrosion of the exhaust system.
No matter what time of year, when starting your vehicle, you should idle for no more than 30 seconds. In fact, I've heard "Click & Clack," the car experts, recommend no more than 20 seconds.
Except when sitting in traffic, turn your engine off if you must wait in your car for more than 30 seconds. You can still operate the radio and windows without the engine running, while saving money.