One Man’s Crusade Against Idling

by Benjamin Jones on September 19, 2008

Image: joiseyshowaa

The other day I spent an hour sitting in traffic in downtown Philadelphia. Not only did I watch my fuel economy plummet on my MPGuino, but I kissed the bumper on a BMW to let an ambulance by, and my car ended up overheating. I was so preoccupied by the traffic that I didn’t notice my temperature gauge creeping up until I finally started seeing smoke pouring out from under the hood. And then I did what any responsible person would’ve done.

I turned the engine off. But, we were in the middle of traffic and there was no way to move the car to the side of the road. I probably could’ve pushed it quite a ways, but not without half of Philly cursing at me for contributing to their traffic jam. So instead of doing parking the car and waiting, I started it back even every time we needed to creep forward and then shut it off instead of idling. The temperature quickly dropped back down to reasonable levels and a crisis was averted.

But then I wondered why I, a person who ecodrives to save gas, wasn’t doing that in the first place. In dense traffic, starting the car back up didn’t slow traffic or me down at all, and all that idling killed my gas mileage. There was just a mental block preventing me from doing the obvious, which is why I was so happy I recently got this bit of encouragement.

An anecdote about idling and fuel savings

The other day, forum member dcb decided to put idling to the test in his commute. While everyone would expect him to save gas by cutting out the idling, he ended up with a surprisingly large 17% gas mileage increase. That’s a real big deal and it came from something as simple as turning off his car when stopped. It’s something everyone can do, and is being incorporated into cars now with start-stop systems so that it can be done automatically.

Of course, no one can promise a 17% increase, that depends on your commute, but any amount of idling that’s cut out will increase your fuel economy. So go ahead, give it a try.

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1 Randy September 19, 2008 at 9:00 am

I’ve done this before. And even left the engine off while creeping ahead while my car was on a down hill slope.

I was SOOOO proud.

I do have two questions:
How hard is it on the car’s starter to restart the engine 20 or 30 times every few miles?

Does it take more gas to start the engine than it does to idle for, say one minute?


2 jamesqf September 19, 2008 at 9:18 am

It’s not hard on the starter at all. That’s an electric motor, so what’s to wear out? It might be hard on the battery if you kept doing start/stop cycles with no chance to recharge.

And it doesn’t take measurably more gas to start a modern fuel-injected engine when it’s warm. If you’ve got an old car with a carburetor, and no feedback loop in the emissions control system, then it might. But the proof is by experiment, as in the article. If someone can drive the same except for not idling, and greatly increase mpg, then how can the car be using more gas to start?

3 Geek September 19, 2008 at 1:27 pm

Well sure. That’s one of the main reasons why hybrids get such good mileage. They auto stop at stop lights and signs. Take your foot off the brake (or clutch) and you’re off again. That saves more gas in city driving than a MPG or two because of aerodynamics or engine design.

4 Rich October 5, 2008 at 8:20 am

2 Decades ago I picked up a fuel saving add-ondevice in a flea market for use on carbies. It had a solenoid to cut-out the idle screw thus cut-off all fuel to the engine when the engine rpm was greater than 500 rpm AND the acceletrator pedal as fully up. i.e. when coasting down a hill, or decelerating, the engine consumed no idle fuel to keep it ticking over. It worked a treat and did save fuel during stop/start city driving, and also during country driving on hilly terrain.
Since then I’ve assumed (but no longer) that EFI in a modern engine would be programmed to do likewise

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