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On Automatic Transmission do you save gas shifting to neutral at stop signs?

I usually drop my car into neutral after hard brakes so I don't warp my rotors, but I think that's about it.
 
Originally posted by: thecoolnessrune
no, because if you are on the brake, the transmission should have disengaged to neutral anyways.
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I don't think you have a firm grasp on how automatic transmissions work. The torque converter will (mostly) stop sending power to the wheels at low RPMs, but the transmission is still connected to the driveshaft whenever you're in 'drive'. It's possible that some cars may do this, but it's definitely not common. Shifting to 'netural' in any AT-equipped car I've driven definitely disengages the transmission and results in lower RPMs (which should use less gas). Turning off the engine saves even more gas if you are going to be stopped for a while.


I wouldn't do it at a stop sign, but if I'm in line at a drive-through or in stop-and-go traffic or at a long red light I sometimes will.
 
Don't you waste more gas by starting the engine after turning it off than by letting it run at idle at a traffic stop?
 
Originally posted by: paulney
Don't you waste more gas by starting the engine after turning it off than by letting it run at idle at a traffic stop?
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I believe this is an old wives tale. It the same about light bulbs using more power when you turn them on.
 
Why wouldn't the engine computer cut off the fuel if you downshift the auto? It should do so, shouldn't it? If so, that would be the way to save gas when slowing down, anyway.
 
Originally posted by: LTC8K6
Why wouldn't the engine computer cut off the fuel if you downshift the auto? It should do so, shouldn't it? If so, that would be the way to save gas when slowing down, anyway.
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That isn't what he asked, though.

It's been my experience that shifting into neutral while stopped causes the engines RPM to go up, not down. Which makes sense, considering it's taking the drivetrain load away from the engine. 😛

Since this is the case, I believe the engine will use more fuel while in neutral. But it is most likely going to be insignificant, both because RPM isn't the only factor in fuel economy and because most stop lights aren't 10 minutes long.

It might be a good idea to do it to save wear on your transmission fluid, though, especially f you live in a hot climate.
 
Originally posted by: Eli
Originally posted by: LTC8K6
Why wouldn't the engine computer cut off the fuel if you downshift the auto? It should do so, shouldn't it? If so, that would be the way to save gas when slowing down, anyway.
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That isn't what he asked, though.

It's been my experience that shifting into neutral while stopped causes the engines RPM to go up, not down. Which makes sense, considering it's taking the drivetrain load away from the engine. 😛

Since this is the case, I believe the engine will use more fuel while in neutral. But it is most likely going to be insignificant, both because RPM isn't the only factor in fuel economy and because most stop lights aren't 10 minutes long.

It might be a good idea to do it to save wear on your transmission fluid, though, especially f you live in a hot climate.
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In reality you aren't going to save any measurable amount of fuel by shifting into neutral at a stoplight. You will certainly use more fuel by coasting in neutral but again, it will be a miniscule amount.

Personally, I'd rather leave the car in gear, that way you have drive if you need to get out of a situation quickly.
 
Originally posted by: JulesMaximus
Originally posted by: Canai
I usually drop my car into neutral after hard brakes so I don't warp my rotors, but I think that's about it.
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WTF? 😕
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I mean after I nearly rear end someone and the brakes are super hot, I put the car in neutral and take my foot off the break to let it cool a bit. My step dad's euro mechanic recommended it, so I dunno if it's necessary or not, but I'm pretty sure it's not hurting anything.

Disclaimer, I know nothing about cars other than what I've learned doing engine work from Chilton books.
 
Originally posted by: chuckywang
Originally posted by: biggestmuff
Originally posted by: JulesMaximus
Originally posted by: Canai
I usually drop my car into neutral after hard brakes so I don't warp my rotors, but I think that's about it.
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WTF? 😕
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No kidding, huh?
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Your brakes have nothing to do with your drivetrain.
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I know that. I'm just saying the only time I put my car in neutral is after braking very hard. 🙂
 
You won't save any measurable amount of fuel doing this. If anything you might put more wear on the tranmission?
 
cmon guys...

brake rotors get hot. hot metal warps. if he heats his brake rotors a ton in a bigtime stop. he puts it in neutral so he doesnt have to keep the brake pressed upon the rotor in one spot for the amount of time that he's sitting idle anyway.

still dont get it? i dont care 😛
 
Originally posted by: tidehigh
cmon guys...

brake rotors get hot. hot metal warps. if he heats his brake rotors a ton in a bigtime stop. he puts it in neutral so he doesnt have to keep the brake pressed upon the rotor in one spot for the amount of time that he's sitting idle anyway.

still dont get it? i dont care 😛
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And what if he needs to use his brakes to keep his car from rolling?
Park would be a better option if he REALLY needed to cool his rotors down.
 
Originally posted by: SampSon
Originally posted by: tidehigh
cmon guys...

brake rotors get hot. hot metal warps. if he heats his brake rotors a ton in a bigtime stop. he puts it in neutral so he doesnt have to keep the brake pressed upon the rotor in one spot for the amount of time that he's sitting idle anyway.

still dont get it? i dont care 😛
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And what if he needs to use his brakes to keep his car from rolling?
Park would be a better option if he REALLY needed to cool his rotors down.
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Yes, if it is at a big incline, it goes into park. Or I just stop far enough back so that I can roll in neutral for the whole light.
 
Originally posted by: Canai
Originally posted by: SampSon
Originally posted by: tidehigh
cmon guys...

brake rotors get hot. hot metal warps. if he heats his brake rotors a ton in a bigtime stop. he puts it in neutral so he doesnt have to keep the brake pressed upon the rotor in one spot for the amount of time that he's sitting idle anyway.

still dont get it? i dont care 😛
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And what if he needs to use his brakes to keep his car from rolling?
Park would be a better option if he REALLY needed to cool his rotors down.
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Yes, if it is at a big incline, it goes into park. Or I just stop far enough back so that I can roll in neutral for the whole light.
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Seems like too much work and too much worrying over something that really isn't a big problem. I've braked hard countless number of times while driving and my rotors have all had long service lives. I doubt that the lack of having your brake pads applied to the rotor after a hard stop will affect the rotors enough to warrant not applying the brakes.

 
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