Coasting in Neutral???

I have 2001 Acura Integra GSR Stick shift, is it safe to just coast in
neutral down hill or will it prematurely wear out my transmission? I
have read about some people who practice hypermiling and alternate
between neutral and drive. What do you guys think?

 

I know that practice is illegal and reduces the amount of control you
have with the vehicle.

 

Define "downhill".

It won't wear out your transmission, but in general it's not safe to
coast for much of any distance. The issue is being ready to accelerate
the car. You have to be in gear to drive it, and if you're not in gear
when you suddenly need to be, you're in trouble.

Also, for long downhills you want engine braking so you want to be in an
appropriate gear that keeps you from using your brakes excessively.
Coasting just gives you a runaway car, and constant braking just wears
out your brakes and possibly overheats them.

 

see what others wrote on legal and wear.

regarding fuel consumption, injection systems cut off fuel delivery
entirely on over-run, i.e. when revs are above say 1,600rpm and there is
no throttle. if the engine is idling, then it's still delivering fuel.
translation: idling uses more gas than engine braking so don't do it.

lots of things you can do to improve mileage. good quality plugs and
ignition system. ensure timing is correct. air filter is good. etc.
and one little thing that i switched onto recently, making sure the tw
sensor works ok. i had a couple in my civic that "tested" ok, but both
were aged, and among other things, caused the computer to think the
motor was colder than it really was, and thus inject more gas. my
mileage has improved about 10% since i replaced it. your car is
reaching a similar age. new ones cost ~$25 from online honda parts dealers.

a new oem honda thermostat is a good idea too, but just for reliability
reasons.

 

This brings up a similar question that I have. My son took over driving my
'97 Civic and when he's rolling down hills, he engages the clutch to "roll
in neutral". I have told him that I didn't think this was a good practice
but can't explain why it might be bad for the clutch. Can someone explain
for me: 1-is this bad for the clutch? and 2-exactly why?
Thanks,
Rosscoe

 

Besides causing premature wear of the throwout bearing from the clutch
being held open for extended periods of time, I can not think of
anything. He will learn to stop doing that when you make him pay for
the rattling throwout bearing!

 

Exactly, premature wear. The same reason it isn't a bad idea to shift
into neutral at a stop light and release the clutch pedal, versus
sitting there in gear holding the clutch pedal to the floor.

And I agree with the comment on coasting in neutral versus remaining
in gear. I typically roll up to a light in the highest gear I can, for
as long as I can until the engine starts to lug, before I disengage
the clutch and allow the car to go into idle. As noted, no fuel is
delivered while you're
coasting in gear, but some is when you're coasting in neutral (i.e.,
engine is idling).

Dan D
'07 Ody EX
Central NJ USA

 

Of course there is fuel being used while coasting in gear. The engine is
still running, is it not? Therefore it's using fuel. No different than
idling in neutral in that respect.

 

Ok what if I am going down a slight hill (not mountain hills) at 40
mpg, then shift to neutral...ride it out for a few seconds then back
in gear so I can go up the next hill? I would stay in gear but that
slows me down so I can't take full advantage of the hill and the
momentum.

How would being in neutral while riding would wear anything out? Can
someone explain that to me in full detail please.

Thanks

 

It's not the neutral part that wears things out, it's the getting back into
gear afterwards that does.

Ever notice how it takes a bit of pushing before the lever will drop back
into gear again? That's your synchros grinding themselves into powder.

If you push the clutch, rev the engine up to where it will ultimately be
and hold it, lift the clutch, push it again, quickly drop the lever into
gear and lift the clutch again, and get all this juuuust right, then there
will be little wear to the synchros.

It's called "double-clutching". Look it up. It adds a lot of fun to driving
a manual transmission.

 

Hmmm,
I thought doulbe-clutching was before the days of synchros. Heck I shift
without cluching, LOL. Those days are over for me too. My concern for
coasting is safety.

 

You think wrongly.

Double-clutching is as relevant today as it was in 1920, and for the same
reasons. But synchros now mask what failure to effectively double-clutch
would have loudly and embarrassingly revealed in 1920.

Part of the reason I got 255,000 miles out of my last clutch is because I
double-clutch every downshift. And after 305,000 miles my synchros work
almost as well now as they did when new.

 

no dude, it's a cone clutch - cone clutches lock solid in next to no
time, incur /very/ little wear, and are incredibly reliable. if you had
a porsche-type baulk ring synchro, you'd be a little more correct
because the wear rate is higher, but again, they last a /long/ time when
everything is working right.

it's entirely unnecessary unless there's something wrong. and that
"something" is usually an uncoordinated driver, or a clutch plate
sticking to the flywheel. uncoordinated drivers chew up transmissions
just as fast, single or double clutching.

 

that bit's not true - it's because you don't slip the clutch. if
anything, operating the springs/bearing twice as often as you need to
/reduces/ life of the mechanical parts.

that may be true, but it's much more likely that it's because you shift
more slowly as a function of the above. synchros are very effective,
and provided the clutch is disengaging properly, have very little load
on shifting. unless raced and slammed prematurely, synchros last as
long as the rest of the transmission.

 

Others have explained the wearing out stuff... Bottom line is, coasting
is a waste of time, won't really give you any benefit, and might actually
cause harm. Just drive along like the rest of us.

 

the engine is rotating, but that's because the momentum of the car is
pushing it. all the pistons are doing is pumping air - the injectors
are not releasing gas unless the ecu says to do so. and in this
situation it doesn't. when the revs drop below threshold again, /then/
it starts to inject, and thus the engine can run on its own. the
transition is seamless and the driver never notices.

nope, it's completely different.

go to megasquirt.info and read through the source code for an injection
computer. all the modules are easy to follow and you'll find the
section where it specifically states the condition for over-run fuel cut
off. enjoy!

 

Hi,
If you knit pick, you are right. Some cars even have a shift light on
the dash signalling time to shift. Tach is there for a reason. Then how
many real drivers are on the road these days? Most are motor vehicle
operators.

 

True, but it's the engine-rev during double-clutching that keeps the clutch
from slipping. I guess you could rev the engine without double-clutching,
but that won't help the synchros.

If there was any additional wear on any of the parts due to double-
clutching, it was undetectable when the old parts were removed. I checked
specifically for that when the clutch was changed.

Let me clarify my statement: Double-clutching extends the life of the
synchros far beyond what it would be if the lever had simply been dragged
into each lower gear without rev-matching. It's that which kills synchros
in addition to too-fast shifting.

 

it does. and that's what you should do. if you've changed gears
without the clutch, you'll find it only works when the engine revs are
in range.

the bits that would wear from double-clutching are the thrust bearing
and the pressure plate mechanism. the friction plates won't be affected.

strictly speaking, too-fast and non-matching are the same thing. for
racing, one of the reasons for lightened flywheel is that engine revs
can change more quickly allowing quicker rev matching, and thus quicker
shifting.

i was reminded of this a few years back when i had both a 91 stick crx
and a 91 stick civic std. the std had a heavier flywheel than the crx,
and the time it took for revs to drop from any given rpm was about
double that of the crx with the lighter flywheel. and thus, you
couldn't shift as quickly. being able to compare the two "side by side"
was actually dramatic in contrast - you had to be considerably more laid
back in the std.

 

All synchro friction surfaces are cones. All synchros have been cones,
and have operated on the same friction principles, ever since the first
ones were installed in the 1928 Cadillac.

All synchro assemblies have baulk/blocker rings of some kind that
prevent engagement of the dog teeth until the two synchro halves are
immobile relative to each other (i.e.: matched). Baulk/blocker rings are
separate from the friction surfaces of the cones, although the female
half of the synchro does form one half of the baulk ring assembly. There
are many, many designs of blocker rings, but all of them operate on
identical principles.

If you feel the lever hang up a bit (or a lot) before dropping into
gear, you are experiencing the baulk/blocker rings in action, protecting
the dogs from the damage they would incur as a consequence of speed
difference relative to each other. The greater the difference in
friction surface rotational speeds, the more drag the synchro friction
surfaces must apply before they are matched, and the longer the baulk
rings will delay dog engagement. Excessive drag from excessive speed
difference can actually burn through the oil film seaprating the two
halves of the cone and cause metal-to-metal wear, which /dramatically/
shortens synchro life.

If the lever drops in immediately under very light pressure, the two
synchro halves were closely matched in speed, and have become quickly
immobile relative to each other. This means the synchros have had little
work to do, and the baulk/blocker rings were not long subject to the
rotational forces that caused them to prevent dog engagement.

The upshot: Proper double-clutching extends the life of the synchro
friction surfaces.