Coasting in neutral doesn't save gas

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On Jul 30, 5:44 pm, snipped-for-privacy@milmac.com (Doug Miller) wrote:
nner.com> wrote:

== And it will stop running so you had might as well have turned off the key. Some automatics don't like to be rotated by the drive train with the ignition off at speeds over 30 or 40 mph and damage can ensue. ==
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wrote:

What you are missing is the engine is being turned over by the wheels through the transmission, with the fuel shut off untill a mi imum engine speed is reached, where the fuel comes back on. In many cases, putting the car in neutral does NOT allow the engine to return to curb idle - it idles at almost the same speed as the engine would be running in gear at the speed you are coasting.. My PT cruiser behaves this way - the idle slows down as the car coasts to a lower speed.
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snipped-for-privacy@snyder.on.ca wrote:

This is what my SUV does. If I put it in neutral while coasting down a hill the engine revs at the RPM the car's computer estimates will cause the least amount of resistance when reengaged. As a matter of fact as the car gains speed rolling down the hill the engine's RPM increase.
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On Jul 30, 12:21 pm, snipped-for-privacy@milmac.com (Doug Miller) wrote:

Coasting the motor idles right, even coasting at 70 downhill the motor is only getting gas to idle, but in gear at 70 it wont be 6-700 rpm it will be maybe 1400 rpm, the increase is drag through the drivetrain not gasolene.
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It doesn't matter what the rpm is; if the injectors aren't delivering any fuel, the engine isn't using any. What part of "the engine doesn't use ANY fuel when coasting in gear" do you find hard to understand? Did you even read the article?
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On Jul 30, 1:21 pm, snipped-for-privacy@milmac.com (Doug Miller) wrote:

WHILE coasting yes, but as someone else tried to explain, coasting in gear will slow the car faster than coasting in neutral. That doesn't matter if you're coasting to a stop, but if you're not, the fact that you've slowed more means you will use more fuel after coasting to regain that lost speed.
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== If people want to coast, then build a soap-box racer and go at it. Driving a car and coasting in neutral or with the key tuned off is just asking for trouble. I would hope these "gas saving" coasters stay off the roads that I travel on. ==
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wrote:

In most areas it is not only dangerous, but illegal to coast with power off - and in many it used to be (don't know if it still is)illegal to coast in neutral.
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How can it NOT be a gasoline consumption issue? Either it save gas or not. Isn't that the point?
If there is a problem with the Popular Mechanics analysis, I'd say it's that they seem to assume you come to a stop at the bottom of the hill. Let's say you're coming down one hill and then going back up another. If you coasted in neutral and allowed the car to pick up additional speed, then at the bottom, that momentum would reduce gas consumption for a brief period when going up the next hill. Of course the problem with that is that you could only pick up a little more speed without things becoming unsafe, you lose engine braking and the gas saved isn't worth it.
Another interesting thing that PM didn't talk about. They said that while going downhill in gear the fuel flow to the injectors is actually zero. If you coasted in neutral, the fuel flow would have to resume so the engine could idle. So, it seems like you could actually use MORE fuel coasting.
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snipped-for-privacy@optonline.net wrote:

That's what they said. Coasting in gear equals zero fuel consumption. Coasting in neutral uses idle speed gas.
Whatever the latter is, it is more than zero.
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http://www.popularmechanics.com/cars/how-to/repair/coasting-in-neutral-fuel-economy?click=pm_news
The guy is an idiot.
My parents owned a 70s Saab Monte Carlo with asperated V4 and positive engagement. When the car was not accelerating, the transmission disengaged entirely from the engine. It could also be switched to normal operation, but got better mileage with the tranny in constant disengaged mode, though it took some getting used to. It also had excellent disc brakes, obviously. I understand there were other cars with this feature. I ended up owning it for awhile. Great car.
nb
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That was one of Saab's two-strokes, right? The thing with two-strokes is the accelerator doesn't just feed the fuel, it feeds the lubricant. Try to engine brake with one and you get high revs with no lube. Then pretty soon you get no revs at all.
See http://en.wikipedia.org/wiki/Freewheel
Chip C Toronto
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== Ain't that the truth... ==
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No. The two stroke was a three cylinder. The V-4's were four cycle.

Joe
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Ah! thanks.
Chip C
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Chip C wrote:

The two-strokes were 3-cylinder inlines. The 96 phased in the Ford Taunus V4 in 1967 and 1968. It didn't need freewheel but Saab kept it.
I'm curious about the author's assertion that a car won't corner without drag or thrust from the engine. If that were true of Saabs, the company would have gotten rid of freewheel. I drove a 96 until 1984. I didn't lock out freewheel because I didn't notice any problem.
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They kept that feature so long? Cool.
Freewheel (I forgot the term-thnx) never bothered the Saab. Besides, it was a Monte Carlo, their sporty model. The guy I sold it to said, "Damn, this thing is good enough to compete in". I think he eventually did.
nb
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notbob wrote:

The one I was driving in 1984 was a 1973. They quit importing them into the US not long after that because the windshield was too close to the driver, although I thought the Saab's shoulder harness made the distance adequate.
In 1966, a friend from high school took me on a trip in his 2-cycle 96. I was impressed, so my parents bought a 1967 V4. They bought a second in 1968.
In February of 1969, my older sisters asked me to drive them and a friend on a weekend visit to Vermont. I wanted to take the 1968 because the radials would hold better on ice. They insisted on taking the 1967 because it had a radio. FM through a 5" speaker made their day.
On the way back we encountered rain after dark. With frost in the ground and the temperature below 35, ice under the water was inevitable unless the road was treated. Where were the sanders? Eventually I recommended stopping at a diner until a sander came by. They wouldn't hear of it.
On a 45 mph highway, I crested a hill at 20. At the bottom, a car had spun and gone through the guard rail. The car was clear of the travel lane and there were probably no serious injuries, but a dozen onlookers were standing in my lane and a truck was coming the other way.
I applied the brakes very lightly and lost traction. I let off the brakes and tried again. It kept happening and I wasn't slowing. Oblivious to the danger I'd warned them about, my sisters demanded, "Quit fooling around!" Eventually I got enough traction to stop. So did the truck behind me.
That's the only time I wondered if locking out a Saab's freewheel would have helped. It wouldn't have mattered with the the 1968. Its radials held better on ice, and its disk brakes seemed to allow better control of light braking than did the leading-shoe drum brakes of the 1967.
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He's assuming at least two things that are wrong: "a rule of thumb for idling fuel consumption is 1 gph"
That is not a rule of thumb, and idling a CAT C-15 set up for 475 hp. doesn't burn anywhere near 1 gph.
Still, coasting in neutral is a bad idea for the control issues alone. -----
- gpsman
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On Fri, 30 Jul 2010 09:29:04 -0500, HeyBub wrote:

fuel-economy?click=pm_news
Most newer cars the OBDII keeps the RPMs up according to the speed, not the pedal. I can shift into neutral while driving say at 35mph and my RPMs won't drop to idle but rather slowly decrease with the speed of the vehicle. I guess this is to limit drive train noise from slack.
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