When is it better to let your car engine idle rather than turning the car off and starting it again?
Fuel perspective: Letting your engine idle for more than 10 seconds consumes more fuel and generates more greenhouse gas emissions than turning it off and starting it up again.
When you let your engine idle to warm up your car, while waiting at a drive-through, or waiting for passengers, your vehicle is needlessly burning fuel.
The estimated fuel consumption of an idling engine is 0.6 litres / hr per litre of engine displacement. This means that an idling 3.5 litre engine consumes more than 2 litres of gas per hour. Letting your engine idle 30 minutes a day for two winter months burns a full tank of gas without ever moving a kilometre!
In winter, the best way to warm your vehicle is to drive it.
Wear and Tear on your Car: Given the usual wear that occurs on the mechanical parts of your car when it starts, it is more economical to turn off your engine when you stop for more than 60 seconds (outside the flow of traffic) and to start it up again when the time comes.