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#1 (permalink) Old 06-01-2008, 07:38 AM
 
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OK to coast downhill in Neutral?

I have several miles of a 7% grade on my drive and wondered if it is OK to the smart transmission to put it in neutral and coast.
Its a highway so once you're at 50 mph at the top of the hill, you'll get to the bottom, 4 miles later, at 65+ mph.
But I'm not sure its appropriate to the various rotating parts if the fluids aren't being pumped or whatever.

Many thanks,
Hamp
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#2 (permalink) Old 06-01-2008, 07:58 AM
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Don't know why you might want to do this; I don't think it will have an impact on fuel economy, and you be more likely to have to use your brakes to control your speed (= more brake pad wear) in the absence of engine braking.
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#3 (permalink) Old 06-01-2008, 08:01 AM
 
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No, it doesn't speed up that much that I'd have to brake. What I do have to do is keep the gas on so the engine doesn't retard and keep me from taking advantage of the hill.

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#4 (permalink) Old 06-01-2008, 08:08 AM
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Garage
Most modern cars with auto tranny will cut fuel to 0 consumption when coasting down hill as aposed to putting the car in neutral and useing fuel to idol the car. Not sure if the smart does this though. The pcm can tell the dif between costing and idoling
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#5 (permalink) Old 06-01-2008, 08:19 AM
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Hey....4 miles for free is worthwhile

Quote:
Originally Posted by hampyoung View Post
I have several miles of a 7% grade on my drive and wondered if it is OK to the smart transmission to put it in neutral and coast.
Its a highway so once you're at 50 mph at the top of the hill, you'll get to the bottom, 4 miles later, at 65+ mph.
But I'm not sure its appropriate to the various rotating parts if the fluids aren't being pumped or whatever.

Many thanks,
Hamp
In my book. I know of people up here who have to commute thru the mountains of VT that coast down the long hills all the time....let it rip!!! As long as you leave the engine idling it will not hurt a thing. These guys who have done that are claiming mileages near 50 mpg with the advantage of coasting. As long as the speed doesn't get up too high....wind drag will keep the speed down to a reasonable number.
Go for it.
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#6 (permalink) Old 06-01-2008, 09:43 AM
 
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I've been coasting in N, too, tho my stretches of road are only a few clicks long ** nowhere NEAR 4 miles! Because I have to switch back fairly quickly (about 30-40 seconds at most), I keep my hand on the shifter whenever I'm in N so that I don't forget to switch back when the road flattens out (or in case I need a burst of speed in some unforeseen emergency).

I have a ScanGauge, and the change is apparent instantly. When I drive downhill, the mileage reads about 45-55 mpg. In neutral, you'd expect the instant mileage to read 9999, but actually it's usually around 130-260 mpg (usually the latter). Still, 256 mpg is a lot better than 56 mpg any day ** even for 40 seconds.
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#7 (permalink) Old 06-01-2008, 10:40 AM
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An old lady's observation:

Back in the dark ages when I was in high school driver's training, one of The Rules for developing safe and sane driving habits was, "Never Coast Downhill in Neutral."

1. Coasting eliminates the duality of braking power; engine braking and The Brakes. Placing the onus enirely on the brake system (pads, drums, etc.) is overtaxing that system, destroying the integral relationship designed to utilize every possbile element for maintaining control over a vehicle.

2. Using your brakes alone generates more heat (energy) which exponentially weakens braking power. The hotter your brakes become, the lower the integrity of your brakes. Mechanical brakes were developed to work with engine braking, not alone.

3. Taking your car out of gear to coast down a mountain jeopardizes your ability to regain engine control in the event of a road hazard. Cars were not designed shift in and out of neutral at driving speeds. Transmissions are highly technical mechanisms, and forcing a shift back into gear while coasting down a grade is imposing a great deal of stress on a *very* expensive component of your car.

Operating your vehicle outside the design parameters increases the liklihood of system failures. Comparing that risk with the nominal savings of fuel usage is irresponsible, in light of the risk to self and others on the road.

One of the responsibilities of driving is to be acutely aware of the dynamics of the infinitely complicated machine being driven, and minimizing the risks involved in its operation by using that machine as it was designed and intended for use. Pushing the edges of the envelope is everyday useage is irresponsible and dangerous.

If all the cars going down a particular mountain grade were in neutral, how safe would you feel?
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#8 (permalink) Old 06-01-2008, 11:03 AM
 
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Quote:
Originally Posted by Susie 1382 View Post
An old lady's observation:

If all the cars going down a particular mountain grade were in neutral, how safe would you feel?
About as safe as skiing, snowboarding, sledding, tobogganing, skydiving, paragliding, soaring, surfing, floating down a lazy river on a sunny day in an innertube with your favorite beverage, or sitting on the banister and riding it to the bottom floor.

I think his point is very specific to a certain situation where brakes are not necessary, the car doesn't become a runaway train, the flow of traffic is at the same speed and we should all assume he's a fully competent individual who is a careful driver unless we know otherwise.

I think his question really is, "Is it OK to shift in and out of Drive and Neutral while rolling?"

I don't have specific knowledge of the answer, but admit to doing it in every car I've ever owned without any damage occuring.

Last edited by Dave777; 06-01-2008 at 12:05 PM.
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#9 (permalink) Old 06-01-2008, 11:36 AM
 
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I chuckled at the engine braking comment.

Last edited by artificial; 09-03-2008 at 12:30 AM.
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#10 (permalink) Old 06-01-2008, 12:11 PM
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Respectfully, comparing coasting down a mountain in a car to skiing down a mountain on two sticks of waxy material is comparing apples to oranges, but does compare equally with the risk of losing control. In the car, the worst case scenario is a deadly crash; the best case, no effect. On skis, same worst case, and likewise best case applies. The difference is that in each worst case outcome, the car poses a far greater threat to other drivers than a human body to other humans on the mountain. Of course, to either, a tree is never a good thing.

The point I was trying to make to younger drivers is that placing all your faith in the abilities of your car to protect you and others is best served by operating the car in it's intended manner. While experienced drivers may feel comfortable free-wheeling in neutral, it is nevertheless a bad practice to develop as a driving style.

Using the skier as an exmple, there are ski runs of different difficulites rated so a skier may determine for himself a comfort level depending upon experience, gear, and willingness to explore his limits and abilities.

Skis strapped onto your feet are a far cry from operating a car.

While I understand there are many instances with favorable outcomes for 'downhill coasters,' there are likewise many instances of lousy outcomes.

The youthful driver who depends upon the advice of the experienced drivers, is better served by the *safest* attitude for operating a motor vehicle, just as the beginning skier is better advised by the experienced skier to 'stick to the bunny hill until you've got the snow-plow down pat.'
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