How Long Should You Idle Before It’s More Economical to Turn Off Your Engine?
This question has intrigued me for a long time–even more so in these days of higher gas prices. I seem to remember that in the polluted Missoula valley where I grew up in the 70’s and 80’s, air quality officials advocated turning off your car if you knew you’d be idling for longer than 30 seconds. That was in the old days of carbureted motors, which were much less efficient to start up again.
Looking around the Internet lately, that recommendation is down around 10 seconds, with the break-even point actually being around 6 or 7 seconds. One reason for shorter recommended idle times is due to the increased efficiency with which modern, fuel-injected motors start. The Green Lantern section of the Slate website (http://www.slate.com/id/2192187/) provides an interesting article on this notion, written by Brendan E. Koerner, entitled “Is an Idle Car the Devil’s Workshop?” The estimated annual savings of this tactic (about $34 a year according to the article) is a little disappointing, but the notion of such a short break-even point is intriguing.