Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Shutting engine off at traffic lights with an automatic transmission

Christ · 10-13-2009, 04:10 AM

If you have to shut off for only a few seconds, no.

Consider the small amount of fuel you use before the PCM enters closed loop mode again, before you get it back into gear, and while you're waiting for the transmission to be actively in gear. You have to defeat that much gas usage to make it worth while, versus the fuel used just idling for a few seconds. You're better off timing the lights, if you can, and preserving momentum as much as possible.

I read somewhere that the cutoff point for one person's car was something like 7.5 seconds of engine-off time to compensate for the fuel used in starting/taking off again. Anything more than 7.5 is black, anything less than 7.5 is red, for that person. I can't say for your car, and it does/will vary with your driving habits.

10-13-2009, 04:10 AM	#4 (permalink)
Christ Moderate your Moderation. Join Date: Nov 2008 Location: Troy, Pa. Posts: 8,919 Pasta - '96 Volkswagen Passat TDi 90 day: 45.22 mpg (US) Thanks: 1,369 Thanked 430 Times in 353 Posts	If you have to shut off for only a few seconds, no. Consider the small amount of fuel you use before the PCM enters closed loop mode again, before you get it back into gear, and while you're waiting for the transmission to be actively in gear. You have to defeat that much gas usage to make it worth while, versus the fuel used just idling for a few seconds. You're better off timing the lights, if you can, and preserving momentum as much as possible. I read somewhere that the cutoff point for one person's car was something like 7.5 seconds of engine-off time to compensate for the fuel used in starting/taking off again. Anything more than 7.5 is black, anything less than 7.5 is red, for that person. I can't say for your car, and it does/will vary with your driving habits. __________________ "¿ʞɐǝɹɟ ɐ ǝɹ,noʎ uǝɥʍ 'ʇı ʇ,usı 'ʎlǝuol s,ʇı"