Coasting in neutral or with clutch down?

[moorecomp]

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.

[elhigh]

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.

[NeilBlanchard]

Hi,

Originally Posted by DIMS

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.

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.

[vtec-e]

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

[99metro]

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.

[jime57]

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 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.

[99metro]

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.

[PaleMelanesian]

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.

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.

[Nevyn]

Originally Posted by 99metro

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.

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.

Originally Posted by jimepting

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.

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?

[DIMS]

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