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Old 01-13-2008, 03:16 PM   #1
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Neutral to drive?

Would putting my car in neutral down a hill and then back into drive have any ill effects on my transmission?
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Old 01-13-2008, 03:29 PM   #2
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no just dont slip it into reverse or park. its called an automatic for a reason.
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Old 01-13-2008, 04:16 PM   #3
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as has been covered many times, it's fine. just don't do it at 90mph so the tranny has to rev the engine from idle to 4k rpm. basically, if you'll end up over about 2k rpm tap the gas a little to bring the revs up before shifting to neutral. this will eliminate any possible wear.

As with any component make sure you change the fluid periodically!!! not changing fluid is the #2 killer of transmissions.
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Old 01-17-2008, 11:50 AM   #4
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If you're going to do this also turn the engine off, otherwise you won't see much of an increase anyhow. I would make sure the foot is off the gas, and I speak from experience when I say you will hit Reverse at least once...
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Old 01-17-2008, 12:44 PM   #5
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Quote:
Originally Posted by 8307c4 View Post
If you're going to do this also turn the engine off...
Consider adding a safety warning or disclaimer when you're talking about an automatic transmission.

Quote:
...otherwise you won't see much of an increase anyhow.
Absolutely incorrect. The most savings come from the neutral glide -- killing the engine is incremental.

If you don't believe that, do the math for yourself. Assume for the sake of argument that an engine burns 0.3GPH at idle. If a driver can manage to neutral glide 25% of the time (and I'd say that's optimistic), 0.075 gallons per hour is the maximum additional fuel savings.

I believe in incremental savings -- a percent here, a half percent there adds up. I'm only saying that leaving the engine on does not make the technique worthless.

Quote:
...I speak from experience when I say you will hit Reverse at least once...
... unless A) your vehicle has a lockout (my VW won't go into reverse if the brake pedal isn't depressed) or B) you pay attention to what you're doing.

Rick

P.S. As long as I'm mentioning disclaimers, I should point out that driving in neutral is technically illegal in a lot of places. Check your applicable laws and make informed decisions.
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Old 01-22-2008, 11:43 AM   #6
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GMC Yukon: Yes Jaguar S-Type: No

I would say any tranny dangers and savings may also depend on the fuel cutout and transmission logic of your particular vehicle. I'm lucky two of my three cars have onboard computers to help me weight the risk vs. the reward.

My 2000 Jaguar S-Type shows no instant mpg computer readout improvement shifting into neutral while coasting down a hill and bangs around a bit returning to drive. This is one I won't coast in neutral since there is no reward for doing so and there appears to be some damage risk.

But I saw dramatic jumps in instant mpg on the computer (99 mpg vs. 45 mpg) with my wife's GMC Yukon XL. Overall, the Yukon XL increased nearly 20% to about 15.3 mpg in its first full week of city driving with coasting in neutral.

Shifting in-and-out of drive is very intuitive if you're used to driving a manual transmission. Returning to drive from neutral usually happens when stopped at a stop light or turning a corner at very low speeds. There is no noticeable bumping or clunking from the tranny, unlike when I use the cruise control, where it often bangs quite dramatically coming out of coast on the highway. Whatever I'm doing to the transmission sure seems safer than what the designers hopefully accounted for in their cruise control system.


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Old 01-22-2008, 05:05 PM   #7
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I coast in neutral whenever I can and it does help the FE ( per ScanGauge). I also rev the engine a little and shift back into drive as the RPM's decline; it feels smoother that way to me.
And I have shifted to reverse but was going really slow and only for a brief moment.I don't think it damaged anything.
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Old 01-22-2008, 08:41 PM   #8
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Quote:
Originally Posted by Rick Rae View Post
If you don't believe that, do the math for yourself. Assume for the sake of argument that an engine burns 0.3GPH at idle. If a driver can manage to neutral glide 25% of the time (and I'd say that's optimistic), 0.075 gallons per hour is the maximum additional fuel savings.

I believe in incremental savings -- a percent here, a half percent there adds up. I'm only saying that leaving the engine on does not make the technique worthless.


... unless A) your vehicle has a lockout (my VW won't go into reverse if the brake pedal isn't depressed) or B) you pay attention to what you're doing.


P.S. As long as I'm mentioning disclaimers, I should point out that driving in neutral is technically illegal in a lot of places. Check your applicable laws and make informed decisions.
No automatic should ever be shifted, if you want disclaimers.

And most fuel engines burn 1/4 tank every 3 hours of idling, that would be a lot closer to a gallon an hour, but for the sake of argument I measure fuel consumption in ounces and I believe that's 2 ounces per minute but really all you're doing is lengthening the time off interval. Only time gliding is profitable is over stretches that last more than a few seconds, I wouldn't bother shifting for less than a 20-30 second glide anyhow, constant gas is as likely to maintain the economy.

You gain a small percent by gliding in neutral because your transmission is no longer creating drag, but the other half of the equation comes from turning the engine off. If small percents matter that much, then turning the engine off certainly should.

Yes, you should let the engine rpm's rest at idle before turning it off.
Better yet don't do it unless coasting to a stop.

Because I am telling you sooner or later you will hit R when coming out of drive.
I didn't say it would happen a lot, it might not happen the first 4-500 times, but sooner or later it will. No matter how careful you are, and if it happens once it happens twice, thou I am sure your perfect driving or your lock out never malfunction.
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Old 01-23-2008, 07:23 AM   #9
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^shouldn't make all-inclusive statements. a metro takes a LOT less fuel to idle than a v8 yukon. most transmissions don't mind it at all if you change the fluid even 200% service interval. some do tho, so do your research. the auto that came in my car has had people do hundreds of redline N-D shifts to do burnouts in cars with over 150k and never missed a beat. I've heard certain manual subaru trannies shatter like glass when you launch in them.

in any auto trans, as stated above and elsewhere, if the manual says you can flat tow it, OK. otherwise you'll fry the transmission in very short order with the engine off.
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Old 01-23-2008, 06:20 PM   #10
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Jaguar S Types have WEAK auto gearboxes, don't try it again One of my friends had this car, and drove it normally, and the gearbox died at 60,000 miles. Also look on Carsurvey.org
Quote:
Originally Posted by MarvHein View Post
My 2000 Jaguar S-Type shows no instant mpg computer readout improvement shifting into neutral while coasting down a hill and bangs around a bit returning to drive. This is one I won't coast in neutral since there is no reward for doing so and there appears to be some damage risk.
Also, in my current car (Bluey II), I get about 120MPG coasting at 40mph (therefore 0.3GPH ish), and almost 200MPG at 62mph.

Going into neutral means that the engine revs *drop* so that, although the injectors are injecting the same amount of fuel per cycle, you get less cycles per second, therefore less fuel is used.

Using neutral has allowed me to significantly increase my economy on short journeys (note that my journeys are getting shorter as I become more efficient at planning routes, timings, as I get used to this country, and get to know the area).

Engine-on neutral coasting is even worth it at 20mph in my car
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