I just came across an article that begs us not to do that. Here's part of what it says:
I was once scolded by someone for NOT idling my car before driving it! I wish I knew that person's email address so I could forward this article! :-)
Although typically ignored or played down by state and even national environmental regulators, more people need to be educated that the best way to warm up your car or truck is to drive it. And studies have shown that frequent restarting has little impact on engine parts such as battery and starter motor.
* Ten seconds of idling can use more fuel than turning off the engine and restarting it. If you are stopped for more than 10 seconds - except in traffic - turn off your engine.
* Every 10 minutes of idling costs you at least 2/10 (0.2) of a gallon of gas - and up about 7/10 (0.7) of a gallon for an 8-cylinder engine. Keep in mind that every gallon of gas you use you produce about 19 pounds of carbon dioxide.
* Exessive idling occurs at drive through windows, drive through bank deposits, and train crossings; while waiting for your kids to get out of school, running into the convenience store, and when picking up your friends for a night out.
A good rule of thumb is: "Idling gets zero miles per gallon."
In the United States and Canada, if every driver avoided idling for just 5 minutes a day, millions of tons of CO2 would be prevented from entering the atmosphere each year. That would represent a staggering contribution to positive climate change efforts...