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Old 04-29-2008, 08:20 AM   #11
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Grill block. Use discarded political sign material spray painted black.
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Old 04-29-2008, 10:50 AM   #12
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I was under the impression that when an automatic shifts from N to D, it starts at 1st gear. Thus, when crusing at higher speeds in N and needing to gain speed again, you'd start at 1st gear (at high rpm, wasting fuel) when putting it back into D, negating any effects of gained fuel economy.

When coming to a stop, you'd rather keep going in D because you can engine brake, saving your brakes, because you know you're going to stop.

Thus, it seems like the only appropriate time to shift into neutral to save gas is when fully stopped at a red light. I guess you could also put it into Park? At the very least, you won't be using your tail lights.
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Old 04-29-2008, 10:58 AM   #13
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Neutral with the parking brake on...
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Old 04-29-2008, 11:55 AM   #14
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Coasting in Neutral will still use gas - at idle level. In some cases, leaving it in gear will trigger fuel cut. But that will also slow you down faster. You have to balance the two as you drive.

Neutral with the engine running is 100% fine. No problem. It's neutral with the engine off that MAY damage an automatic transmission. Some are ok, some are not. If the owner's manual allows flat 4-wheel towing, then it's fine.

If you rev-match before shifting back into drive, there should be no jolt or anything - smoother than a system-controlled shift.

Coasting in neutral, engine on or off, is a critical part of getting super-high mileage. Pulse & Glide.

Grill Block is a good one. Use anything and everything that will fit. Some people use foam pipe insulation stuffed in the slots.
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Old 04-29-2008, 12:09 PM   #15
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Quote:
Originally Posted by RoadWarrior View Post
Because most cars since the early 90s have had injector shutoff above certain RPM when the throttle is closed. Ergo, you could be using more gas idling the motor than letting it engine brake.
In this case, how is a manual trans better? Is there no injector shutoff in a car with a manual transmission?

In other words, if we have 2 cars that are identical except the transmission, putting the trans in "N" and coasting will yield no benefit whatsoever. Correct?

This means there are - maybe - 2 prime benefits to having a manual trans:

1. Ability to pick shift points to maximize FE.
2. Lower mechanical losses.

(personally, I prefer the stick shift because it's more fun to drive)
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Old 04-29-2008, 12:16 PM   #16
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3. you can bump-start a manual.
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Old 04-29-2008, 01:14 PM   #17
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Quote:
Originally Posted by FLAteam View Post
I was under the impression that when an automatic shifts from N to D, it starts at 1st gear.
Mine has never done this, and I doubt any would. It should go to an appropriate gear. I've often shifted between N and D at every speed up to at least 75 and never had it enter D at 1st gear. I've done it in at least 7 different vehicles, probably more.

Even if you found one that does, it would immediately shift to a more appropriate gear, before you even had a chance to apply the gas pedal.

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When coming to a stop, you'd rather keep going in D because you can engine brake, saving your brakes, because you know you're going to stop.
Saving brakes is a negligable savings. How much brake life do you expect to save? Could you get 10% more brake life? Brake service generally costs between $50 and $200 and lasts between 20,000 and 100,000 miles...

Most automatic transmissions I've used won't use a low enough gear for engine braking when in D. However, if yours at least keeps the engine above 1000 rpm while coasting in D, you'll most likely get DFCO (Deceleration Fuel Cut Off), meaning no fuel is used during that time. If it has a towing, power, or sport mode, it might downshift more aggressively; I've been experimenting with switching to "Tow/Haul" mode in my truck while decelerating but it's not helping, I have to just shift it down to 3 and 2 myself.

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Thus, it seems like the only appropriate time to shift into neutral to save gas is when fully stopped at a red light. I guess you could also put it into Park? At the very least, you won't be using your tail lights.
Agreed.

Quote:
Originally Posted by PaleMelanesian View Post
If you rev-match before shifting back into drive, there should be no jolt or anything - smoother than a system-controlled shift.
Wouldn't rev-matching waste gas? The torque converter always buffers the N->D shift comfortably for me.

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Grill Block is a good one. Use anything and everything that will fit. Some people use foam pipe insulation stuffed in the slots.
I'm new here, can you direct me to a thread or document about grill blocking? I've seen it in a few posts and I'm curious as to how and why it helps.

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Originally Posted by dosco View Post
In this case, how is a manual trans better? Is there no injector shutoff in a car with a manual transmission?
There is injector shutoff (DFCO). A manual transmission allows you to use DFCO much more easily.

Quote:
In other words, if we have 2 cars that are identical except the transmission, putting the trans in "N" and coasting will yield no benefit whatsoever. Correct?
Doing so requires fuel usage to keep the engine idling. I prefer DFCO to keep it from using any fuel, but I have not yet experimented with a pulse+glide technique, where N would probably be more appropriate.
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Old 04-30-2008, 07:44 AM   #18
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Originally Posted by theholycow View Post
I'm new here, can you direct me to a thread or document about grill blocking? I've seen it in a few posts and I'm curious as to how and why it helps.
Use the search function. Basically it is an aerodynamic modification to "block" the airflow into some or most of the front end grill. Many/most cars have more duct area (cross sectional area of the grill inlet) than they need for normal use.

Quote:
There is injector shutoff (DFCO). A manual transmission allows you to use DFCO much more easily.

Doing so requires fuel usage to keep the engine idling. I prefer DFCO to keep it from using any fuel, but I have not yet experimented with a pulse+glide technique, where N would probably be more appropriate.
So what you're telling me is that when I'm driving on the highway in my '99 Camry and take my foot off the gas, that the engine is essentially "off?" Not sure I buy that because I would expect MUCH more engine drag and therefore deceleration.

The next question is how is it "easier" to use DFCO in a stick vice an automatic? Are you suggesting that one would downshift at highway speed to take advantage of the DFCO?

Another question is about pulse and glide. Where, exactly, is the efficiency gain made? Is the idea to run the engine at its most efficient RPM followed by use of the cutoff?

Let me state that I've started to experiment with shifting to "N" where it seems logical. I have some data from my first fill-up, but I think I screwed the pooch b/c I didn't top off to "1 click" (my usual fill-up procedure) and my estimate of fuel used could be wrong. Reason I think this is that I do have data from last year indicating my typical mileage was 27 to 31 MPG, whereas my most recent data show 25 MPG (although the higher mileage was with August temperatures in the metro DC area).
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Old 04-30-2008, 08:37 AM   #19
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Quote:
Originally Posted by dosco View Post
So what you're telling me is that when I'm driving on the highway in my '99 Camry and take my foot off the gas, that the engine is essentially "off?" Not sure I buy that because I would expect MUCH more engine drag and therefore deceleration.
It took me a while and a lot of discussions before I quite believed it. I assumed there would be more noise/vibration from the engine. However, if you think about it, everything is still running, there's just no fuel being injected.

Unless you have an extremely low top gear, there will be little drag just letting the wheels turn the engine. Think about all the torque required for the engine to turn the wheels in that gear; from the wheel's point of view, it's very easy to turn the engine.

This is why people trying to start the engine by rolling the car and popping the clutch use 3rd gear instead of 1st, and why you park a manual transmission in 1st instead of 3rd, 4th, or 5th.

Quote:
The next question is how is it "easier" to use DFCO in a stick vice an automatic? Are you suggesting that one would downshift at highway speed to take advantage of the DFCO?
I've never feared shifting between N, D, 3, 2, and 1 on the highway. I've never driven a Camry, but I have driven a Tundra. I don't remember if I've tried it in the Tundra though I certainly wouldn't be afraid to. I seriously doubt Toyota would expose themselves to lawsuits and recalls to save five minutes worth of writing code or designing the valve body.

If it's a floor mounted shifter, you can probably move between D and N without pressing the button on the shifter. Consider that it's common for someone's elbow to accidentally knock it into N (as I once did in my mom's Ford Probe in 1988, scaring her since she was afraid to shift between N and D at highway speed); they would have required you to press the button if it was dangerous, as they require to shift out of P or from N to R.

However, I doubt that you'll need to at highway speeds unless your top gear is super tall. Below 1000 rpm is probably the point where DFCO quits, so as long as you're coasting in gear above 1000 rpm it's probably in DFCO mode. With an auto, if the torque converter isn't locked, then you'll have to coast faster to keep it above 1000 rpm than with a manual or an automated manual such as a SMT/DSG. I doubt there's any vehicle that won't keep it above 1000 rpm at 65 mph.

Sorry I can't answer any question about pulse & glide, I could only offer an educated guess. I need to learn about it too. I've intuitively done it sometimes, though.
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Old 04-30-2008, 08:51 AM   #20
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Quote:
Originally Posted by theholycow View Post
This is why people trying to start the engine by rolling the car and popping the clutch use 3rd gear instead of 1st, and why you park a manual transmission in 1st instead of 3rd, 4th, or 5th.
I understand all that, no problemo.


Quote:
I've never feared shifting between N, D, 3, 2, and 1 on the highway.
Not sure if you read my long-winded post, but I've been experimenting with shifting to "N" from "D." No problem.

My question is why do you think it is "easier" to employ DFCO with a stick rather than an automatic?
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