How long is too long to keep your car idling?
 

Is there a general rule of thumb that says you shouldnt leave your car idling for a certain amount of time? I know some people who will actually turn their cars off if they are stuck at a railroad crossing with a long train. The most I think I have ever let my car idle was for about 5 minutes. I dont let it run if Im in the house doing something or if I go into the store (if someone is in the car) and so on.

Modern cars could probably idle forever, but older cars and especially carburetted cars will foul the plugs if you idle for too long.









I turn the engine off if I'm going to be idling for more than 10 seconds or so. You don't use all that much fuel starting the engine these days.

It takes very little to keep an engine running also. It will do no harm to idle a modern car until it runs out of gas. The only reasons to shut it off are to save gas and to avoid having it stolen while you are not in the driver's seat.