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Old 07-27-2007, 02:01 PM   #1
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Gas consumption at idle

I am debating whether shutting the engine off at stop lights is worth the gas savings. Does anyone know what the fuel flow at idle is for my 2007 Toyota Corolla when its fully warmed up? Or any other 1.8 liter 4 cyl?
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Old 07-27-2007, 02:05 PM   #2
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'A lot' ; if you have fuel economy feedback you will see the mileage go down quickly when you are stopped with the engine idling!.

My car, at idle, uses as much fuel as it would take to move at about 15-20mph! My car is a 1.8, fuel injection, but isn't that efficient.
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Old 07-27-2007, 02:07 PM   #3
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What do you use the car for? Do you have a daily commute? Often you can make big savings, without 'extreme' techniques, just by considering factors in your daily commute!
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Old 07-27-2007, 02:31 PM   #4
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My 4 cyl 2.2l consumes 0.2 gallons per hour in idle (in neutral 725rpm, 0.3 in D) according to the ScanGauge. I shut off the engine when it seems like I can do it for more than 10 seconds. There are a few long lights that I know in town that as I approach I can estimate how long I need to wait. Usually that means shutting down and gliding to the red, waiting, then turning on when it's green again.

I think it definately benefits because if I idle, the trip MPG on the ScanGauge is going down 0.1mpg every few seconds.
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Old 07-27-2007, 02:53 PM   #5
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That sounds pretty good, Andy; my 2.0l (AT) uses 0.3GPH at an 800ish RPM idle.

If I switch over to l/h for better resolution, I can see that it uses about 10% less idling in neutral than in drive (same RPMs but the engine's free-wheeling instead of fighting the torque converter). So at lights that aren't long enough to shut the engine down, I at least drop it into neutral to save a little bit.

By the way, that dropping MPG figure is asymptotic to zero so, thankfully, the longer/more often you get stuck idling, the more slowly it will drop (and the more miles you have on the reading the more slowly it'll change, too). I think that's what makes it maddening: You work so diligently to push the number upward, and as soon as you stop at a light and idle, it begins falling off at the fastest rate it's going to for that trip from that point onward!

Rick

P.S. I presume you meant 0.2 gallons per hour. Otherwise I can see why your numbers are falling so fast.
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Old 07-27-2007, 03:05 PM   #6
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Oh I meant gallons per minute. I measure out a 25 ounce gatorade bottle with gas and just throw it out the window every minute

I should find out again, I'm almost positive it was 725rpm at 0.2gph in N, unknown rpm, 0.3gph in D.
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Old 07-27-2007, 03:28 PM   #7
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Quote:
Originally Posted by GeekGuyAndy View Post
I should find out again, I'm almost positive it was 725rpm at 0.2gph in N, unknown rpm, 0.3gph in D.
I believe you. I was just appreciating that your displacement is 10% more than mine, yet your idle consumption is lower. I used to drive a Subaru but I don't remember it being particularly efficient.

As for the difference between drive and neutral, the measurement granularity might be getting you. If you're using 0.301 GPH in drive and 0.299 GPH in neutral, for example, the SG's resolution limit might make the difference look much larger.

If you decide to recheck it, you can try switching to liters for more resolution, then convert liters to gallons. (I can't see any difference at all between idling in drive and neutral when my SG's set to gallons.)

Rick
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