Shifting to Neutral on an A/T - Better FC?

[jut703]

Using the same car, in the same driving conditions, my mother garners 6.6-7.1 km/l. When my dad used the car for a week, his average was 8-9 km/l, and they both pass the Makati-Pasig route. This is despite the fact that he drives at an average speed 20 kph faster and has occasional bursts of boy racer tendencies.

I would attest the lower FC of my dad to the fact that he keeps a more constant and less hasty acceleration from standstill, but he also does one quirky thing - he frequently puts the car in Neutral when coasting.

Is this bad for the car? It's an Altis 2.0V A/T. Also, I've noticed that when taking the foot off the gas, the rev drops to 1000 rpm. Does that mean that even in D, when the pedal is disengaged, the car goes to neutral? In other words, is the act of shifting to N every time you coast unnecessary?

And, does shifting to N actually help improve fuel economy? If so, at what cost? Does it drastically increase the wear and tear of the transmission?

I'd just like to be informed, so that I'll know if I should follow it or if I should advise him to stop, especially since my mom now does the same thing too after I told her my dad gets better mileage.

[KinKyHOOTER]

Using the same car, in the same driving conditions, my mother garners 6.6-7.1 km/l. When my dad used the car for a week, his average was 8-9 km/l, and they both pass the Makati-Pasig route. This is despite the fact that he drives at an average speed 20 kph faster and has occasional bursts of boy racer tendencies.

I would attest the lower FC of my dad to the fact that he keeps a more constant and less hasty acceleration from standstill, but he also does one quirky thing - he frequently puts the car in Neutral when coasting.

Is this bad for the car? It's an Altis 2.0V A/T. Also, I've noticed that when taking the foot off the gas, the rev drops to 1000 rpm. Does that mean that even in D, when the pedal is disengaged, the car goes to neutral? In other words, is the act of shifting to N every time you coast unnecessary?

And, does shifting to N actually help improve fuel economy? If so, at what cost? Does it drastically increase the wear and tear of the transmission?

I'd just like to be informed, so that I'll know if I should follow it or if I should advise him to stop, especially since my mom now does the same thing too after I told her my dad gets better mileage.

I don't thing putting the A/T to N will give dramatic increase to fuel consumption. You will actually waste the momentum you have gained from 1st, 2nd, 3rd, 4th gear....at 70kph, the VVTi will kick-in and it will limit your RPM between 1,500 - 1,800 RPM. So from that speed the VVTi is actually helping you conserve the energy and speed gained from accelration. Then after coasting at N from 80kph, you let the speed go down to 30kph...then put the tranny in D again and have the engine rev again and accelerate to 80kph. Sayang ang energy and momentum gained by the car. The Engine actually works the hardest while accelerating, and having a heavy foot to couple it with will result in bad fuel mileage.

Two additional things:
====================
1.) If you put A/T transmission to D from N while at speed (80kph example) will jolt the tranny as it engages the gears again and that is also not good.

2.) Coasting at N will also be dangerous as it will not have engine brakes.

I think the better fuel mileage your dad is getting is a result of him having a lighter foot on the gas pedal compared to your mom.

[ParticleX]

i coast also (going N on downhills) on a terrano to help the turbo cool it down, but sometimes i worry about the brakes will conk out anytime (with the huge weight of the vehicle ). i think it would be better to stay with D, the fuel savings is not worth it compare to an engine brake, who knows what will happen.

[HardCharger]

I read somewhere that doing this is bad for the transmission.

It has something to do with the tranny fluid circulation and the sudden load thing mentioned.

It's also discouraged because of the also mentioned lack of engine breaking.

[niky]

Going downhill, it's better to leave it in gear. With your foot off the gas and the throttle plate closed, your engine is either using miniscule amounts of fuel or absolutely no fuel (if it's EFI, the injectors shut off completely on coast-down).

For this reason, actually shifting to N while driving doesn't really help much... unless you're practicing hypermiling and using the "Pulse and Glide" method. (which also requires you to turn off your engine... ). If you're coasting to a slow stop, coasting in gear once you're below around 60 km/h uses no gas, whereas if you're coasting in neutral, you'll use more fuel because your engine is still idling.

Shifting to neutral does help, though, at a stop or in stop-go traffic... at a stop, your torque converter is under load, straining against your brakes. In stop-go traffic, putting it in "N" after you move allows you to coast a bit farther with just a little tap of the gas.

Many nay-sayers say that the extra motion wears down the mechanism... but if the torque converter is disengaged when you shift, there's really no issue.

[jut703]

I don't thing putting the A/T to N will give dramatic increase to fuel consumption. You will actually waste the momentum you have gained from 1st, 2nd, 3rd, 4th gear....at 70kph, the VVTi will kick-in and it will limit your RPM between 1,500 - 1,800 RPM. So from that speed the VVTi is actually helping you conserve the energy and speed gained from accelration. Then after coasting at N from 80kph, you let the speed go down to 30kph...then put the tranny in D again and have the engine rev again and accelerate to 80kph. Sayang ang energy and momentum gained by the car. The Engine actually works the hardest while accelerating, and having a heavy foot to couple it with will result in bad fuel mileage.

Two additional things:
====================
1.) If you put A/T transmission to D from N while at speed (80kph example) will jolt the tranny as it engages the gears again and that is also not good.

2.) Coasting at N will also be dangerous as it will not have engine brakes.

I think the better fuel mileage your dad is getting is a result of him having a lighter foot on the gas pedal compared to your mom.

He only coasts during, for example, on the downhill part of the flyover. Shifting back from N to D right after doesn't give any jolt as you say. Or are you talking about a jolt unfelt by occupants but present in the transmission?

The issue about wasting energy on acceleration after shifting back to D isn't actually much of an issue, particularly because he shifts to N mostly when going downhill, where the car even accelerates, or if he's slowing to a stop (For example a stop light, around 500m from it he releases the gas, shifts to N, and brakes to a stop).

Going downhill, it's better to leave it in gear. With your foot off the gas and the throttle plate closed, your engine is either using miniscule amounts of fuel or absolutely no fuel (if it's EFI, the injectors shut off completely on coast-down).

For this reason, actually shifting to N while driving doesn't really help much... unless you're practicing hypermiling and using the "Pulse and Glide" method. (which also requires you to turn off your engine... ). If you're coasting to a slow stop, coasting in gear once you're below around 60 km/h uses no gas, whereas if you're coasting in neutral, you'll use more fuel because your engine is still idling.

Shifting to neutral does help, though, at a stop or in stop-go traffic... at a stop, your torque converter is under load, straining against your brakes. In stop-go traffic, putting it in "N" after you move allows you to coast a bit farther with just a little tap of the gas.

Many nay-sayers say that the extra motion wears down the mechanism... but if the torque converter is disengaged when you shift, there's really no issue.

So from my understanding, for example going down a flyover, and I'm going at 80 kph. If I just release the accelerator, I wouldn't be feeding my engine more fuel even if the downhill slope increases my speed to about 100 kph? In other words, I don't need to shift to neutral to cut the fuel off since it does so already as long as I keep my foot off the accelerator? And in fact, if I understand correctly, keeping it in neutral uses more fuel because of the idling?

And does going through successive humps count as stop and go. There's this street near our place where there are about 7 humps in a 500 meter stretch, and what he does, upon approaching the hump, shifts to N, then once the car overcomes the hump, shifts to D, taps on the gas a little just to keep the car moving, then shifts back to N and coasts until the next hump. Is this better for mileage or is it just better to keep coasting?

In fact, I don't really understand the concept of Neutral and Drive that much when it comes to how it consumes fuel. If I am moving and I put the car in neutral, I'm using the same amount of gas as I would if I were idling on a stoplight, yes? But, releasing the gas pedal while in D completely cuts fuel supply to the engine? Is that why, when I'm driving, whatever the slope, as long as I coast while in D, my revs go down to 1000 rpm? I mean, driving a manual and releasing the gas keeps the rpm at whatever rpm it is until it slowly decelerates. Apparently it's not the case for automatics and I don't particularly understand why.

[mreyes]

sir niky,

is this called hypermiling? ginagawa ko rin ito pero nung nabasa kong nakakasira ng auto tranny, di ko na ginagawa. lagi na lang akong nasa D, and would only put it in neutral pag trapik or pag nakahinto sa trapik light.

[Type 100]

So from my understanding, for example going down a flyover, and I'm going at 80 kph. If I just release the accelerator, I wouldn't be feeding my engine more fuel even if the downhill slope increases my speed to about 100 kph? In other words, I don't need to shift to neutral to cut the fuel off since it does so already as long as I keep my foot off the accelerator? And in fact, if I understand correctly, keeping it in neutral uses more fuel because of the idling?

One big yes.

And does going through successive humps count as stop and go. There's this street near our place where there are about 7 humps in a 500 meter stretch, and what he does, upon approaching the hump, shifts to N, then once the car overcomes the hump, shifts to D, taps on the gas a little just to keep the car moving, then shifts back to N and coasts until the next hump. Is this better for mileage or is it just better to keep coasting?

No, that does not count as stop-and-go. Think about it: you're not coming to a complete stop every time you come across a hump. You WANT to press the throttle to crest the hump and go along your merry way, so why would you want to put it in Neutral in that situation?

It doesn't make sense. If anything it overcomplicates things. The less you have to fiddle with the controls, generally the better for the car.

[KinKyHOOTER]

He only coasts during, for example, on the downhill part of the flyover. Shifting back from N to D right after doesn't give any jolt as you say. Or are you talking about a jolt unfelt by occupants but present in the transmission?

The issue about wasting energy on acceleration after shifting back to D isn't actually much of an issue, particularly because he shifts to N mostly when going downhill, where the car even accelerates, or if he's slowing to a stop (For example a stop light, around 500m from it he releases the gas, shifts to N, and brakes to a stop).

Ah I see. So your dad is just doing the coasting before every stoplight Stops. Well actually it does make the engine consume less gas, but not that much at all compared to having it in D before every stoplight Stops. No major gains really as I see it.....its the same with going from D to N before every humps.

But its actually dangerous, because if you need to do sudden
maneuvers you wont be able to do it because your in N.

The jolt to the tranny thing that I mentioned was because I thought your dad was coasting from stop up to a speed (ex: 80kph) then putting it to N then after the speed gets slower he puts it to D again, the driver will feel a little jolt once the gear engages again. Nothing disastrous really, but I feel its not good for the tranny...I understood your question wrongly earlier

----> Yes, putting the car to N is in the same state as if your idling in your garage or on every stoplight.

----> While in D, even if you dont step on the gas the automatic tranny is still engage. On a level ground, it will still move even if you dont step on the gas........I'm not very sure, but I think it still consumes gas and still has a 4th gear engine brake effect. Please correct me if I'm wrong.

[Type 100]

But its actually dangerous, because if you need to do sudden
maneuvers you wont be able to do it because your in N.

The jolt to the tranny thing that I mentioned was because I thought your dad was coasting from stop up to a speed (ex: 80kph) then putting it to N then after the speed gets slower he puts it to D again, the driver will feel a little jolt once the gear engages again. Nothing disastrous really, but I feel its not good for the tranny...I understood your question wrongly earlier

Agreed on the inability to do sudden maneuvers.

Shifting from N to D at speed is also not good for your A/T. On a manual gearbox you could blip the throttle before re-engaging the clutch to avoid driveline wear, but on an A/T the clutch is permanently engaged.