Idle or Restart the Car - Which Saves More Gas?

I don't own a car anymore, but there was a time when I would sit in the drive-thru at a fast food restaurant or wait in line at the toll booth and see fumes rising up from all the cars as they patiently idled. 

Watching all those wavy lines rise into the atmosphere, I wondered whether it was better to turn the car off or to let it run. I figured it is possible that restarting the car over and over would actually burn more fuel than just letting it idle for a minute while I waited. 

Today I found the answer to this puzzle on Slate.com's "Green Lantern" column. A reader wrote in, asking the Green Lantern to settle a marital dispute over the possible fuel savings of turning a car off rather than leaving it to idle. 

According to the Green Lantern, the idea that your car uses more fuel restarting than idling is outdated. A long time ago, cars used carburetors to flush fuel into the engine to start the car. However, all modern cars use electric fuel injectors which carefully measure the amount of fuel necessary to start the car. 

To prove the point, a study conducted by the American Society of Mechanical Engineers in Florida showed that unless you are idling your car for six seconds or less, turning the engine off will use less fuel. This study used as its test subject a six-cylinder car with the air-conditioning on. 

Another idle myth that can be smashed is the idea that your car needs to "warm up" in cold weather when it is first turned on. This isn't the case. The best thing for your car is to begin driving immediately after the engine is turned on. The Ontario Department of Transportation performed an experiment where they found that a car driven for 12 minutes in 14 degree (fahrenheit) conditions will warm up to the same level as a car idling for 30 minutes.

The Green Lantern estimates that if all Americans turned their engines off, rather than idling, for 10 minutes per day, the combined savings in carbon dioxide emissions would be miniscule. However, if all cars were updated with the same technology the Toyota Prius currently includes, we could reduce national fuel consumption by 10%. The technology in the Prius turns the engine off instantly any time the car comes to a halt. Pushing the accelerator turns the engine back on. This means that in traffic, at traffic lights, at the toll booth, etc., your car would be conserving gasoline. 

To read the full Green Lantern explanation on Slate.com, go HERE

1 comment:

  1. Thanks for the comments!!! My husband and I totally agree, we try to encourage all our friends and our family to turn their engines off. I wish there was a way to get through to people who think it is ok to warm up their vehicles in the winter and cool them off in the summer, that it pollutes our precious air. But more importantly, it is dangerous. My cousin and I were left in an idling vehicle when we were only 4 years old and my cousin somehow got the car into gear and it rolled out of the driveway, finally hitting the foundation of a house being built across the street causing quite a bit of damage. Thank God no one was hurt. I still can't imagine how horrified my aunt must have been when she came back out of the house.