OK to coast downhill in Neutral?

[Dave777]

Relative to the ScanGauge...in gear, coasting downhill, the ScanGauge shows 0.0 on the fuel flow. In Neutral, coasting downhill, the engine is idling so will always show a small fuel flow. The question then becomes, "Is it better to coast with the engine running in idle, or leave it in gear and, in the above writer's specific example, add just a little bit of power to overcome the compressive drag of the engine at idle?"

Who knows? It's a tiny fraction of a MPG probably, depending on the total length of his drive, and I personally have no issue with either technique.

[hampyoung]

Lets assume for the discussion that the car doesn't even close to speeds where you would need to brake - because that seems to be a concern for some folks here.
Its a wide open stretch, little traffic, clear view, no tailgaters **- plenty of time to "DRIVE" your car where you want to go, whether you use the engine or momentum. Heck, if we can't handle a car when its coasting (ie: approaching any stop sign/light or traffic), what would make it easier/better/safer to handle when it under direct engine power?
I'm simply trying to learn whether using neutral OK for the engine ** not whether its an appropriate driving technique.
SO, the question is still this: is it OK for the transmission and any other moving parts to be free wheeling (similar to towing the car, yes?) when an appropriate hill for coasting in neutral presents itself.

Hamp

[jefferios]

I'm not going to do it (going downhill in nuetral) When I did it yesturday going about 55mph, and I moved back into D. When I did I got a huge rev in engine power and I was magically down to gear #3. I think the engine was built to coast as well as drive, and not build to drive/neutral/DRIVE.

Plus I don't want to replace my brake pads/rotors for $500+ every 2 years.

[hampyoung]

And one more clarification... assumption.
That you would increase the engine revs a bit before shifting into Drive from Neutral so you match the engine revs to your actual speed.

H

[Dave777]

Originally Posted by hampyoung

And one more clarification... assumption.
That you would increase the engine revs a bit before shifting into Drive from Neutral so you match the engine revs to your actual speed.

H

Understood, of course.

[orngandblack]

Originally Posted by hampyoung

And one more clarification... assumption.
That you would increase the engine revs a bit before shifting into Drive from Neutral so you match the engine revs to your actual speed.

H

Why don't you just do it, and report back what you find??

[hampyoung]

Originally Posted by orngandblack

Why don't you just do it, and report back what you find??

Well, I've done it once or twice and it seems fine ... but I'm not a transmission psychic!
;)

H

[Capt. Jack]

Thanks for this conversation. Here in FL there are no downhills, but I've often wondered about just coasting in Neutral. I haven't heard any official word from 'smart'. Is there any? (Other than the usual 'CYA'...which we're not really interested in anyway.) Since it's a clutch, I'm thinking to go for it. I remember one stretch going out of AZ into CA, or somewhere out there in that vast expanse of sand, that in my '73 Saab 99, I just kicked it into neutral, and actually turned the car off (yeah I know...no PS, PB, etc. whatever). Anyhow, it was a memorable 9 miles of coasting between 45 and 70mph. I'm thinking the smart could do this with no problems...but I would keep the engine on and at idle this time.

[madbunny]

I've got a few hills I'd like to do this on, but they're fairly short so the gas savings isn't significant, but the thing that does annoy me is that engine braking is actually pretty significant. In my GMC Pickup which is probably less aerodynamically efficient, I can simply let off the gas at the top of the hill and it'll coast down the hill nicely. The pickup is an Automatic. Compare this with my Smart where I'd let off the gas and if I kept it let off, I'd slow down from 50 to about 30 at which point it would shift down..etc.
They should have a manual compression release so you can keep it in gear and keep the fuel flow at zero.
I was also told that shifting back into Drive while moving wasn't a good idea, but someone else in another thread said he'd been doing it alot...I think he was told it was okay as long as your foot was off the gas.
So far the only thing I've been doing is popping it into neutral to coast up to a stop, but I have had to put it back into drive once or twice when I misjudged the stop and the light changed back to green(and someone was on my butt). It's seemed to do okay, but I'm very hesitant at shifting back in at highway speeds.
Driving in neutral is certainly more dangerous in some small way, but IMO it's very minor compared to driving behavior that I see all the time like tailgating, passing on blind corners, and even not passing when you have a mile of clear space just because you can see a car in the other lane(shows a serious lack of judgment because they usually pass on the next blind corner). How many people know that they can shift an automatic down to slow up if their brakes fail? How many people know that many brake systems have some kind of secondary system that works if you mash the pedal all the way to the floor?
That's not to say that I encourage or condone "Caucasian Overdrive" (I can make fun of my own ethnicity, right?), but I'm certainly not going to worry about my own safety if 5-10% of the drivers were to suddenly choose to do so.

-eric

[mmmeat]

Originally Posted by hampyoung

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.

Probably not. Fluids won't flow the same in the tranny, the computer could decide to shift gears for you to what it thinks is the appropriate gear when you jam it back in drive, and you're adding unnecessary stress to the clutch - which could end up costing you more in the long run when you have to go in and get a new clutch.

Plus, most of the MBz vehicles I've been in will keep the revs up higher anyway until the car is below a certain speed.

So no, it's not appropriate. And it's not OK. Unless you're planning on getting rid of the car before things start breaking in the drivetrain.

Your pal,
Meat.