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Old 09-01-2009, 06:49 PM   #1 (permalink)
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Time spent at traffic lights - Engine OFF

Hey ecomodders,

I've been lurking about reading as much as I can. Tightening the nut behind the wheel was the single most beneficial MPG increase that I have made 26mpg prior to averaging 36mpgs now.

I have been shutting down the engine when I know that a traffic light is going to be long, and have read that it take about 11 secs. for the mpg benefit to set in. While sitting at traffic lights and counting in my head the amount of time the car is off, I figured I needed a stop watch to find out how much time I am off during the day.

Please understand I am a Field Service Engineer for IBM and drive a lot. This is my first attempt to make a contribution to this site.

Honda Accord 2.3l Auto

Todays numbers:

125 miles

27 Traffic light stops with engine shut down.

22:27 Time spent with engine off.

27 restarts @ .11 secs = 297secs inefficient start recoup


so I think I was shut down for 17:30

my scangauge says I burn .25gph at idle.


Is this worth it?


Is this valuable information to be tracking?

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Old 09-01-2009, 07:08 PM   #2 (permalink)
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Ive been thinking about this as well and while I like the idea of saving fuel, I wonder how much fuel Im really saving with engine off at lights (of course every little bit helps and over time it will add up). My drives are probably far less hampered when it comes to time spent sitting, and I would be suprised if I would be able to actually save even 1/2 gallon of fuel over a complete tank, but others mileage will of course vary. I think the main improvement of engine off use is when coasting up to a red light from a distance and then continuing to sit with the engine off until its time to restart. Thats where you get the biggest gains assuming the car can be safely EOC'd.
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Old 09-01-2009, 10:01 PM   #3 (permalink)
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I don't know about the 11 second thing. I do know that if it's a new car and the starter is expensive it's probably not worth it. The best thing you can do is EOC coast up to the light, and never stop. Popping the clutch to restart is a good idea to.
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Old 09-01-2009, 10:21 PM   #4 (permalink)
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I think this depends a lot on the vehicle. In your case with the low GPH numbers you see at idle it may take a while for the savings to really add up(with luck it covers the new starter and then some). In the case of my Jeep I run about 0.79GPH idle. So it's sucking the gas like none other. So I have found short trips across town(about 5-6miles) it pushes the trip avg up 1-2MPG's if I turn it off at a 20-30second light.

I'm sure others may say it's not worth it. Claim it doesn't counter-act the cost of a new starter. But there are a lot of factors to take in to account, like the fact that in your case you spent 17:30 with the engine off, so the engine will last longer. If you want to get in to the nitty gritty, think about the money you just saved, how much intrest will that earn if you put it in the bank now to cover the new starter down the road?
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Last edited by FastPlastic; 09-01-2009 at 11:44 PM..
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Old 09-02-2009, 12:54 AM   #5 (permalink)
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...I don't shut off the engine at stop lights (need A/C when it's 100 F outside), but I have been "sensitized" to the fact that GASOLINE is "...going away..." while no MILES are being traveled, because the MPG digits keep "ticking" downward...slowly at first (short light) then rapidly (l-o-n-g lights).

...didn't realize I could "hate" stop lights so much (wink,wink)!

Last edited by gone-ot; 09-02-2009 at 01:12 AM..
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Old 09-02-2009, 12:54 AM   #6 (permalink)
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Really, when was the last time anyone had to replace a starter?

VW Rabbits had chronically weak starters, but since those late 70's / early 80's vintage vehicles, I've never had to.

I understand Wayne wore out the starter in his Accord, but the number of starts on his will vastly outnumber the typical ecodriver.

Not saying it can't happen, but I bet it's pretty unlikely.
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Old 09-02-2009, 01:11 AM   #7 (permalink)
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Agree with Metro on the likelihood of replacing a starter...not likely.

And if the OP drives alot...imagine how much fuel he is saving by not idling the engine for 20 minutes a day. If you save a half gallon of fuel a week that's 26 gallons a year or more than $70 a year...just by simply turning your car off at lights. Well worth it in my opinion and just another piece in the puzzle to raising mpg, saving money, helping the environment.
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Old 09-02-2009, 01:46 AM   #8 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
Really, when was the last time anyone had to replace a starter?

VW Rabbits had chronically weak starters, but since those late 70's / early 80's vintage vehicles, I've never had to.

I understand Wayne wore out the starter in his Accord, but the number of starts on his will vastly outnumber the typical ecodriver.

Not saying it can't happen, but I bet it's pretty unlikely.
Just to be a stick in the mud here - I just had to buy a new starter for the wife's Saturn. It had nothing to do with wear, though. Damn corrosion weakened the wire studs on the solenoid, and no one sells just the solenoid.
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Old 09-02-2009, 01:00 PM   #9 (permalink)
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I did the math comparing NICE-on coasting with FASing, and idling while coasting can drop mileage from 60 mpg to 40 mpg. It's going to be worse when you're not even moving.

I found on my cross-country trip that shutting the engine off, but leaving the fan on, kept me cool through even 5 minute stoplights in FL and TX in my Scion. My Nissan isn't as effective, so 3 minutes is about the comfort limit.
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Old 09-02-2009, 02:52 PM   #10 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
Really, when was the last time anyone had to replace a starter?

VW Rabbits had chronically weak starters, but since those late 70's / early 80's vintage vehicles, I've never had to.

I understand Wayne wore out the starter in his Accord, but the number of starts on his will vastly outnumber the typical ecodriver.

Not saying it can't happen, but I bet it's pretty unlikely.
Well, I've had to replace starters on several of my cars - 1988 Chevy Celebrity, 1995 Chevy Beretta, 2000 Chevy Impala. Granted, all of them were beyond 100,000 miles at the time of the replacement, but I take it more or less for granted that I'm going to have to replace a starter at least once.

Note that the above replacements were made before I made it a point to turn the engine off at long lights.

For what it's worth, BMW's owners manuals claim that four seconds of idling is the break-even point for idling versus shutting off. Of course, shutting down and starting up for every 4-second delay sounds like you're asking for trouble. My rule is that I'll shut down if I know the wait will be more than 20 seconds AND if the oil is at operating temperature.

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