Coasting in neutral or with clutch down?
 

Hi I'm new to this forum and hypermiling, I really enjoy the reading.

On my glide I don't go in neutral i rather clutch down its just less work then shifting manual into neutral. What is really better with a diesel?

I doubt it makes much of a difference, to be perfectly honest, but I generally do it with the clutch in in case I need to be in gear.

I always switch to neutral by habit. Some people might say you're wearing your throwout bearing running with the clutch when coasting. But on the other hand I've never heard of someone who really had a bad throwout bearing because of that.

I agree. I always shift to neutral and let the clutch back out.

falfa -

I agree with KJSatz and tasdrouille. I have heard that keeping the clutch pedal pushed down for a long time is "bad", but I can't remember the reason.

CarloSW2

Welcome to the boards!

+1 for the throwout bearing story.

If you are lazy like me, just go into neutral without using the clutch. Its pretty easy to do, you basically just have to eliminate the load on the tranny, which means the engine is not accelerating or decelerating the car. So maybe 10% throttle or so. Depends on your car (truck?) but to get a feel for it, take your foot off the gas, pull on the shifter a tad in the direction of neutral, and give the gas pedal a gentle "blip" and it should pop right outta gear. Easy.

I also shift to neutral. However, if I know my glide is going to be short, up a hill for instance, I'll just use the clutch.

Hi,

I think it depends on the car -- my xA's clutch spring is a little too light, so I don't like to hold the clutch down long; and I shift into neutral to coast. My previous cars with standard shifts (2002 Focus ZX-5, 1987 Golf, and 1970 Volvo 144) this was not an issue, so I held down the clutch as long as I liked.

neutral in my car = less economy
 

The scan gauge gooes off the chart with the car in gear and pedal off the gas, but in neutral it is similar to idle. It appears that I have a fuel cut off in gear but not in neutral.

DIMS: that's normal. But it's generally considered more efficient to go to neutral because your glides will go much, much further in N than while decelerating with engine braking/fuel cut in gear.

I'm with Leanburninating: I can't remember the last time I used the clutch to shift to neutral. Light pressure on the shifter as the transmission unloads, and it shifts out of gear like butter. I rarely glide with the clutch in.

For all but the shortest glides, I use neutral. I don't want to put wear on the the throwout and my clutch is hydraulic, I don't want a slow bleed of pressure to slip the clutch. Notice how the brake pedal goes down when the master cylinder has a pressure leak? My car actually uses half of the brake fluid reservoir for the hydraulic clutch.

I always go to neutral. It's a little less safe, but if you're seriously hypermiling, you're spotting pretty far ahead on the traffic, so you're working with a bigger "traffic picture" than the typical driver. Fewer surprises = more time to anticipate and get your gear back.

Hi,

There are (at least) two types of coasting:

1) In neutral (or EOC) you go a long distance and try to carry your speed as far as possible. This yields very high mileage (up to 380mpg in my car).

2) And the type you are talking about is when you want to slow down, and use the engine to slow down instead of (or in addition to) the brakes. This uses the fuel cutoff and you get "infinite" mileage, but only for the short(er) distances.

Since i switched both my cars to diesel i find that i coast in neutral far less. This is due to the much smaller deceleration experienced because of the lack of a throttle plate. If i'm on a reasonably steep downhill i just come off the accelerator and let it DFCO. I more or less maintain my speed and my injectors are off. Same as a gas engine but i don't slow down as much. If the downhill is less, i coast in neutral with the clutch out. I'd definitely be concerned about the throwout bearing long term. To take it out of gear i do the same as others have mentioned here. That is; i come off the throttle and keep a slight pressure on the gear lever so as to pull it out of gear. When the load and rpm's are right, it just comes out without any effort. Bear in mind that it doesn't work too well if you are already in DFCO as the slight engine braking will oppose all but brute force on the gear lever. And we're not about brute force here are we??!!?? (only during maintenance....sometimes!)

ollie

If I am in traffic, I'll glide with the clutch in to time the greens. Out in the middle of nowhere when I'm coasting to stop signs, I'll stay in neutral and give my clutch foot a rest.

I've gone almost 60k miles on this JDM engine. I'm sure my throw-out bearing will wear out one day, but it hasn't yet. I can see being in stop and go NYC traffic you'd probably wear out a lot of stuff. Longer commutes and very little shifting? - well, that is a judgment call.

I have to defend the design engineers on this question. The throwout bearing in most cars is rather small and not designed for continuous duty at all. Therefore, IMO, one should go to neutral when coasting either engine-on or engine-off. As someone remarked it is very easy to slip the out of gear by applying slight pressure when the throttle is lifted. This practice, when done with a bit of skill, causes no extra wear at all. Of course, the reverse procedure, going into gear without clutching, is bound to be difficult and cause damage.

Incidently, neutral engine-on coasting probably delivers worse FE than engine-on coasting in gear on most modern cars. As mentioned earlier lots of newer cars will go into fuel cut-off when deaccelerating in gear. Go to neutral and you are stuck with engine idle consumption if the engine is on.

So, if you want to experiment with coasting, slip the transmission into neutral, shut off the engine, coast, clutch and re-engage 4th, bump start. I continue to believe that the process imposes some extra wear, but apparently many folks have gotten away with it for years:D I would not do it unless the benefit/wear equation is clearly positive. That is to say, I would only do it if the coast was reasonably long. Otherwise, you are just hammering your equipment for nothing.

I think I know of what I speak. In my racing program I built lots of engines and transmissions.

Just my opinion...

I have heard lots said about fuel cutoff when in gear and the throttle off. I have a hard time believing that the fuel is stopped completely. This would mean the engine is rotating with just the spark plugs firing.

I think what is really meant by fuel cutoff is that the engine is still being delivered fuel, but at the "idle" rpm fuel delivery rate. Anyone who has left the clutch out while decelerating knows that the engine will attempt to maintain idle speed once the idle rpm is met. The car will continue to motor on forever and a day on level pavement if you let it with the vehicle in gear and no throttle. You can essentially let the clutch out slow enough when completely stopped in first gear, and the engine will allow the car to accelerate to near idle rpm even though there is no throttle applied. This is also assuming the idle speed is set to factory specs.

Whether one decides to "glide" while in gear/clutch out allowing engine compression deceleration, or whether in neutral/clutch out and long coasting with the engine at idle speed, is up to the individual person. I know we can argue all day long about this topic, but it all depends on how one prefers to hypermile and the risks you are willing to take for the extra MPG.

Just my opinion - and I'm sure I will be proven wrong.

That's true during that instant, but when you look at the whole trip, the balance tips the other way. I've tested pulse-and-DFCO against pulse-and-neutral idle and against steady speed driving. The results:

Best: pulse and EOC
Good: pulse and neutral idle glide
Ok: steady speed
Worst: pulse and DFCO

You only want to use DFCO if you're needing to lose speed, like coming up to a red light, or down a mountain. Any other time, it's a net loss in mileage. The drag from engine braking overwhelms the gains from no fuel being used.

My honda does DFCO down to 1200 rpm, and below that it restarts the fuel flow. You can feel a surge when this happens.

It stops ignition too. My car will DFCO. The RPM's go up when I drop a gear, and then there is a little "blip" and at the same speed, they drop by about 300 RPM. Once it's down to ~11 RPM, the tach suddenly freefalls to about 400, and then bounces back up to 1400 or so.
DFCO does produce better mileage in the short run...but that's the thing. It's SHORT. Glides at least for me are about 1/3 to 1/5 as long as coasting in neutral. So yes, I'm getting 9999 MPG when in DFCO, but only for say 200 feet, instead of something like 150 MPG for 1000 feet.

I hope that clears some things up?:thumbup:

Acronyms??
 

I guess I'm not up to speed on the Acronyms, Please help :)

Either way (neutral/ICE-on* or DFCO**) you have to get the engine turning. In practice, neutral with it idling has been found to be more efficient. I can give you two reasons why that is the case.

i. Certain conditions must be met for DFCO, including a minimum RPM generally greater than idle speed (often the minimum is in the range of 1000-1500RPM). Thus the DFCO procedure involves rotating the engine more than the neutral procedure, and that extra rotation comes from extra momentum your car loses as you DFCO. Additionally, here you can see why a car can "creep" in first gear: eventually, your engine drops under the minimum threshold, and then fuel is injected, causing creeping.

ii. For neutral, you are burning gas to make the engine turn. For DFCO, you burnt gas in the past that (unfortunately with imperfect efficiency) contributed to your forward momentum that you are now using to make the engine turn. The additional step makes additional work-by-inefficiency inevitable, and so DFCO must be less efficient.

* Coasting in neutral with your engine running at idle.
** Deceleration fuel-injector cut off: under certain conditions, when the car is in gear and you take your foot off the gas, fuel injectors are shut off (zero fuel usage at that moment), and you "engine brake."

Please supply data!
 

What is meant by Best, Good, Ok and Worst? Do you have data to help us understand the testing procedure and the end results data?

No formal testing on this one. Just trying each enough until patterns start to emerge. Then, I focus on maximizing the one that works best. There is definitely value in controlled testing, but for my purposes of minimized fuel usage, I want to find the relative merits of different methods quickly and then move on.

For a given drive, like my daily commute, the different driving styles will give you gas mileage in the order listed. Pulse-and-glide gives me the best, while pulse and DFCO is the worst. As they say, Your Mileage May Vary. An automatic transmission car with decent gear ratios may do much better at steady speed, compared to my manual with short (high rpm) gearing.

Ok, Thanks for the reply
 

Thanks for being honest. Any chance that you remember what the difference between Best and Worst was?

Best you can see in my signature, because that's how I drive all the time.

I've seen 45 mpg on the highway with the cruise control at 65. Pulse and DFCO was lower than that.

Is that better/worse/the same for the clutch? You're not pressing your clutch in which seems like it would be good, but wouldn't it make your tranny more upset (or at least have more of a possibility if you miss your throttle blipping)?

There's no problem or wear moving OUT of gear without the clutch. All you're doing is pulling the gears apart. It's going into gear where it might be an issue.

I can do clutchless shifting if I want to, but usually I use the clutch.

Thanks alot for all good comments.

That the engine goes into fuel cut-off when when coasting in gear, is that also for diesel?

I could never have figured out that putting a gearbox in neutral without clutch and then gear back to 6th after would be more healthy then holding the clutch down.

So for a diesel:

Coasting in gear for breaking
Coasting with clutch in for short distances
Coasting with neutral for long distances

My last car was an 89 BMW 325i. It was a higher compression motor then my honda, but at one point I had an issue with a fuel pump relay intermittently cutting off fuel to the motor for a second or two... it felt like I was hitting the brakes, it would really startle me. I have to guess that this "fuel cutoff" mode gives at least a tiny bit of gas... But Im not a doctor.

As with the whole shifting with or without clutch... like stated already, shifting out of gear and into neutral without the clutch is pretty easy and if you do it right, it feels no different than using the clutch. The shifter will slide into neutral with no bumping or grinding. I would say any wear this causes is negligible. With a little practice you can get it right every time.

Shifting back into gear from neutral is a bit more tricky but still can be mastered. If you said THAT was bad for the transmissions lifespan.. I would say, if done frequently and incorrectly, yes. You just have to get a bit more intimate with your tranny. haha. When in neutral, look at your tach and try to predict where your RPMs would be in Xth gear at your current speed, and if you are perfectly right, the shifter will slide right into that gear. This takes lots of finesse.

Any way you choose to do it, I don't think the time it takes to use the clutch or shifter is a big deal. I think trying to say one is better or safer is splitting hairs. But do try to avoid riding the clutch (.02)

Gas (Petrol), Diesel, LPG.. Im pretty sure its the same for everything. If your not accelerating the engine gets either idle fuel or no fuel (Depending on engine, electronics, make(Ford, dodge.. etc) etc).

As for the coasting, that sounds about right. I suggest keeping your foot over the clutch and a hand on the gear stick when coasting in neutral. Saves a second or so when having to go back in gear.

o.k. your priority list is probably right, for most cars. The thing that bothers me about pulse and EOC is that it involves a lot of extra cycles on the clutch and transmission. Neither were designed for this use. One has to question whether the added fuel economy is worth the extra wear. Not to me, but that's just one opinion. I suppose that for short competition it makes sense, but not for day-in-day-out activity. I still maintain that method 1 has to impose a fairly heavy wear load.

Incidently, EOC=engine off coasting, DFCO= decelleration fuel cut off, FAS= forced auto stop. Many of these acronyms are defined in the glossary link on:

CleanMPG, An authoritative source on fuel economy and hypermiling

Popular Mechanics (No data just assumptions)
 

Neutral Shift for Better Fuel Economy - Popular Mechanics

Q: I have a question about fuel economy. If you are driving downhill, do you save gas by putting your transmission in Neutral and coasting, instead of having your vehicle in Drive? I think that you do but my wife seems to disagree. Can you give me the correct answer, so I can tell her that I’m “Mr. Right,” as usual?

A: That depends. The engine isn’t braking the car going downhill if the transmission is in Neutral, so economy would seem to be high. But if you think the engine is still using fuel while coasting downhill in gear, you’re laboring under a misconception. Most fuel-injected cars turn the fuel delivery completely off when you lift your foot from the accelerator. They still burn fuel when idling in Neutral, so do the math. The amount of fuel burned at idle over, say, a couple of miles of coasting downhill is small, but it’s still more than zero. So if you’re driving a modern fuel-injected car, you’re wrong.

Older, carbureted cars would suck gas through the engine while coasting in gear, even if you turned off the ignition switch. In this case you’d be right.

Hi,

If you want to carry speed as long as possible, then coasting in neutral is best.

If you want to slow down, before you use the brakes, use the engine to slow the car by downshifting into a lower gear.

Yeah, in this case I could disagree with Popular Mechanics's conclusion. Unless there's a stopsign in the near future.

More testing needed :)
 

I'm not sure how far I actually coast in 5th gear to slow down for stop signs and stop lights. I need to figure out my average distance. I also need to figure the time it takes to get close to a stop. I usually leave my car in 5th gear until I get close to a stop. Then the next step would be using neutral method. For me, I think using in gear (5th) will result in the better economy, because just prior to my destination the car goes in closed loop. Putting it in neutral raises the RPMs but using that energy in 5th gear actually propels the car. I think this is one of those cases where different situations require different driving techniques. (one size does not fit all)


In the last 3 months I have driven my bicycle more than my cars.

Who over at Popular Mechanics is writing this stuff? Nothing written so far is right or wrong, so anyone saying it is right or wrong doesn't know what they're talking about or is just guessing. For one, carbs can haz fuel cuts too. Numero dos is that unless the car can stay above the engine speed needed for the fuel cut, it'll more or less idle in gear, and even if the driver accelerates above the fuel cut every time they drop below it then they would have to compare the fuel usage to whatever was used when it idled down the hill. In short, it depends on the car, weather, hill, etc... So the only correct response w/o more information would be "That depends." with all the other erroneous stuff left out.

RIDING THE CLUTCH
All transmission bearings are cooled by an oil bath that draws heat away and replenishes lubricant. A transmission could care less whether you are in neutral or in a gear. But all throw-out bearings are sealed and self-contained. They have no provision for cooling or lubrication replenishment. Therefore, riding the throw-out bearing for extended periods gets it hot. When the throw-out bearing gets hot, two things happen: 1) the grease thins and 2) the oil seals soften. There is a point where the hot, thin grease can make its way past the soft oil seals and escape. If too much grease is lost over time, the throw-out bearing will seize. When this happens, the outer race of the bearing, which is usually stationary, will spin on the clutch forks. This will wear the clutch fork, causing the clutch to fall out of adjustment and necessitating replacement of the fork. Even worse, the inner race of the throw-out bearing will drag on the release fingers of the pressure plate. Eventually they will wear away or break off, throwing debris into the clutch/flywheel/pressure plate interface, scarring up the flywheel. This requires flywheel removal, resurfacing or replacement.

My experience over many years as both a mechanic and heavy truck driver is NEVER hold the clutch down for longer than it takes to shift - or you will eventually be paying a mechanic all the money you saved (by coasting with the clutch in) to repair your clutch assembly.

COASTING IN NEUTRAL WITH AUTOMATIC TRANSMISSIONS
Never do this. Always "coast" in drive. If you have been doing this in a car that the manual does not specifically say can be "flat towed," you should sell your car.

COASTING IN NEUTRAL WITH MANUAL TRANSMISSIONS
In heavy vehicles, coasting in neutral is extremely dangerous and should never be done. In lightweight vehicles, coasting in neutral has little significance as a control issue and provides the greatest mpg gain possible.

I have reviewed the posts on this thread and would like to point out that it does not take much fuel to idle an engine that is not doing work. If you are coasting, you are receiving a tremendous advantage regardless of whether or not the engine is running. Of course, there is an advantage to having the engine off altogether, but on modern cars this disables other systems like power brakes, power stteering, airbags and brake lights and is therefore not an option. Also, you do not want to pop a dead engine back to life at speed because it is stressful on the components and wears the clutch excessively. It is better to start the engine with the key, rev the engine to match the transmission engagement point and engage. Neophytes can locate this point by very lightly touching the shift lever without engaging the clutch, delicately and slowly revving the engine, and feeling the teeth in the transmission slow down as they approach the mesh point. NEVER engage without tapping the clutch until you get really good at this, for two reasons. One, imperfect matching will wear the brass surfaces of the synchro rings excessively and, two, you can break off a tooth which can destroy the entire transmission.

I have to disagree with this. My rear wheels have NOTHING to do with my transmission. 95% of us with autos have FWD, and rear wheels don't do a thing for the transmission.

Alright, I edited out the references to what drives the lubrication pumps. Unless your car can be "flat-towed", an automatic transmission will not receive proper lubrication and could prematurely fail, so the point still applies.

See the thread Solution for coasting an automatic transmission: external oil pump http://ecomodder.com/forum/showthrea...pump-4149.html

But don't go to the trouble on a transmission that's been coasted extensively. It could already be near failure.

alright well that confuses me... when you coast in neutral versus drive on an automatic... your wheel speed stays the same or slowly decreases (you are coasting), its your engine speed that drops.

I would see your point if it was the other way around, that your tranny pump was run off your engine. But if your tranny pump is run off the wheels then it shouldnt matter what the engine/tranny is doing, drive or neutral... where am I wrong?