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Old 03-10-2010, 12:31 PM   #1 (permalink)
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Red light Nuetral Help or hurt?

I've started putting whatever car I'm driving in nuetral at red lights The theory behind it is when your car is in drive it wants to pull a little so it strains your engine by trying to pull therefore using gas However when it's Not in Drive it wont pull at all?

What do you guys think any legitamite increase behind this? even if it's 1/10 of an MPG it'd still be worth it right?

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Old 03-10-2010, 12:49 PM   #2 (permalink)
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According to my Scanguage II, my 3.0l Mitsubishi uses about .45 gph idling in drive once warm. In Neutral it uses 0.35 gph.

My initial thought on the subject is that by slowing down the engine it would use less fuel. Which is probably applicable to carburators, not sure.

New cars with Idle Air Control valves try to keep a constant idle rpm. So when you load the engine down in gear, it opens a small secondary throttle & gives it more go juice.

This is only my thoughts, if they are wrong, someone please correct me.

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Old 03-10-2010, 12:50 PM   #3 (permalink)
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Assuming you're talking about an automatic, most automatics idle slightly lower in neutral than they do in drive. So yes, you'll be using less gas than you would by holding the brake down. Probably nothing too noticeable, but it's better than nothing.

I always put it in neutral in automatics because my first car developed a pretty big rattle when it was stopped in drive, but it went away when I put it in neutral, so it's just a habit now.
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Old 03-10-2010, 01:01 PM   #4 (permalink)
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Quote:
Originally Posted by DonR View Post
According to my Scanguage II, my 3.0l Mitsubishi uses about .45 gph idling in drive once warm. In Neutral it uses 0.35 gph.

My initial thought on the subject is that by slowing down the engine it would use less fuel. Which is probably applicable to carburators, not sure.

New cars with Idle Air Control valves try to keep a constant idle rpm. So when you load the engine down in gear, it opens a small secondary throttle & gives it more go juice.

This is only my thoughts, if they are wrong, someone please correct me.

Don
Carb will still use more fuel because the engine is partially loaded, so it needs more power at either the same speed or even a lower speed to maintain it's condition (running). More power out = more fuel in.

IACV's are the only idle source on FI cars, the throttle plate is fully closed when you're not using the pedal, so the IACV just opens further to compensate for load.

Regarding OP's question - It does use less fuel, but not as much less as just shutting your car off. If you can time the light and shut the engine off and coast up to the light from 500 feet away (provided you're going to sit at it anyway), you'll save several seconds worth of fuel until the opposing light turns yellow, then you restart and you're ready to go by the time your light is green again.

Either method is relatively little gain, but they both work to some extent. I almost always coast to lights. Hell, I turn the engine off when I'm coasting to bleed off speed.
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Old 03-10-2010, 02:30 PM   #5 (permalink)
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So christ what ur saying is it's an alright idea?
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Old 03-10-2010, 04:37 PM   #6 (permalink)
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If you prefer a simplistic answer, yes.

You're not in danger of hurting anything by doing it, and it can save you fuel, although minimal.
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Old 03-10-2010, 05:48 PM   #7 (permalink)
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It can't hurt, it can only help.

I've been doing it for decades but not primarily to save gas. The worst enemy of an automatic transmission is heat. If you can take a load off the transmission, especially in summer, so much the better. Considering that rebuilding a tranny is one of the most expensive repairs, I like to avoid problems. I also drain and refill it every six months. Transmission fluid is relatively cheap - again it can't hurt, it can only help.
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Old 03-10-2010, 06:00 PM   #8 (permalink)
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Quote:
Originally Posted by Thymeclock View Post
It can't hurt, it can only help.

I've been doing it for decades but not primarily to save gas. The worst enemy of an automatic transmission is heat. If you can take a load off the transmission, especially in summer, so much the better. Considering that rebuilding a tranny is one of the most expensive repairs, I like to avoid problems. I also drain and refill it every six months. Transmission fluid is relatively cheap - again it can't hurt, it can only help.
Some think that this might actually hurt more than help... I'm on the fence about that, but I do think it's a waste of money. In six months, unless you drive cross-country twice a month, you haven't even broken in good fluid.

That's where the thought that it does more harm than good comes from. If the fluid isn't broken in (additive package isn't fully released), it's not working as well as it could.

Considering that the only time I ever change fluid or filter is if I have to pull the engine, axle, etc... something that will cause fluid to leak out, which is seldom and far between, I don't think it's really necessary to change the fluid even as often as the MFG says it is (60k, is it?). I've never had an auto fail, and I beat the hell out of them.
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Old 03-10-2010, 06:02 PM   #9 (permalink)
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The new Hyundai/Kia 6 speed AT shifts automatically into neutral when stopped. The AT in the Mitsu Outlander does it too. If the OEMs do it, you can be sure it works.
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Old 03-10-2010, 10:06 PM   #10 (permalink)
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With an auto in a fuel injected car, it will help. In neutral, there is less load on the engine, so it can throttle back and feed less fuel to maintain the same idle RPM. With a carb, the difference is minimal, as the throttle is basically unchanged, just the RPMs due to load.

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