AT netural downhill

steve1ddd · 03-16-2012, 01:07 PM

Excuse the dumb question but i really dont know much about car engines.
I have an 09 370 with Automatic Trans.
I live up in the mountains and my trip down is all down hill. In my previous car which was a stick, i jsut coasted down in netural. is it bad to do this with an AT. Its about 20 miles and i dont have to put it back into gear but maybe 1 or 2 times brienfly? is there even a benifit to doing this (like saving gas?) I do notice i am able to build up more speed while not in gear and thus can coast longer. please advise.

harman.khinda · 03-16-2012, 01:13 PM

leave it in gear. when your coating downhill in gear their is some resistance because the wheels are driving the engine and therefore the engine is using less fuel to keep running. as opposed to putting in neutral and coasting the engine has to idle under its own power.

nepali · 03-16-2012, 01:14 PM

Quote:

Originally Posted by steve1ddd

Excuse the dumb question but i really dont know much about car engines.
I have an 09 370 with Automatic Trans.
I live up in the mountains and my trip down is all down hill. In my previous car which was a stick, i jsut coasted down in netural. is it bad to do this with an AT. Its about 20 miles and i dont have to put it back into gear but maybe 1 or 2 times brienfly? is there even a benifit to doing this (like saving gas?) I do notice i am able to build up more speed while not in gear and thus can coast longer. please advise.

What if that 1-2 times you need the gears immediately but cannot react fast enough?

steve1ddd · 03-16-2012, 01:18 PM

Quote:

Originally Posted by harman.khinda

leave it in gear. when your coating downhill in gear their is some resistance because the wheels are driving the engine and therefore the engine is using less fuel to keep running. as opposed to putting in neutral and coasting the engine has to idle under its own power.

Is this true? i am using MORE gas while coasting? never would have guessed that. thanks for the advise

harman.khinda · 03-16-2012, 01:38 PM

Quote:

Originally Posted by nepali

What if that 1-2 times you need the gears immediately but cannot react fast enough?

hypothetically - turning off your car as you cost downhill and then turning it back on at the bottom would save the most gas.

Felix 808 · 03-16-2012, 02:09 PM

Actually I am going to say it is a bad practice on a few reasons.

1. You never tow an automatic with wheels on the ground in neutral- The trans pump is not pumping vital fluid for cooling. Coasting in neutral would simulate the same conditions, causing excess heat (#1 AT destroyer).

2. Delay in power if you need to gain speed for any reason

$.02 YMMV

fuct · 03-16-2012, 05:51 PM

Quote:

Originally Posted by harman.khinda

hypothetically - turning off your car as you cost downhill and then turning it back on at the bottom would save the most gas.

prob not. the amount of gas needed for the initial fire up might be more than the total used to coast.

but yea, dont coast in any car manual or auto. its bad for the tranny

harman.khinda · 03-17-2012, 11:20 AM

touche'

Augustus · 03-17-2012, 12:45 PM

Don't ever put a transmission in neutral when coasting downhill. Automatic or manual. Doing so is dangerous for several reasons; already mentioned above.

There's also the element of brakes. In the mountains, you want to be using lower gears to maintain speeds down hills. Constant braking down a long slope is a good way to boil your brake fluid and potentially lose all braking. Never mind a lot of added wear and tear on your brake pads.

I am fairly sure this is all in the owners manual.

And Yes, you'll get better gas mileage with it in gear because the injectors can shut down. When idling, youre always using gas.

roy'sz · 03-18-2012, 08:05 PM

coasing downhill in gear does not save you gas because your rpms will be higher in gear rather than idle, if it weren't then that is one tall gear that you have. True that distance+time will decifer what you would save in fuel. If you know your rpm/gear ratio then you could match it fine, or leav it in sport mode and downshift. Obiviously that all pretty much applies to a manual. As for a automatic, if you are coasint in neutral and the car is running, you are providing transmission fluid cirulation. Not a good idea to coast though in neutral because when you put it back into drive the car has to find what gear you are in and it will most of the time start from 1st all the way to 7.

Jordo! · 03-18-2012, 09:15 PM

Throttle off in any gear, injectors are not firing. Thus, same gas mileage.

So, just throttle off in gear and coast.

roplusbee · 03-18-2012, 10:26 PM

I am assuming that you can use the sport shift (or whatever they call it) to engage 3rd or 4th gear to keep a semi-constant speed while "coasting" so that you are saving brakes, keeping power at the ready, and minimizing drivetrain damage. I am not aware of how the drivetrain gets damage rolling in neutral, but the manual states that the car should not be towed in neutral. I was always taught to keep the car in gear while moving, unless you are at the point of stopping.

wilsonp · 03-18-2012, 11:28 PM

As Click and Clack point out, new brake pads are cheaper than a new transmission, so don't put extra wear and tear on the drivetrain for slowing down on hills. Use the parts as they are intended.

roy'sz · 03-19-2012, 12:36 AM

fuel pump puts out pressure to open the injectors for any type of combustion, if they aren't opening then how is it that the engine is running?

roplusbee · 03-19-2012, 06:41 PM

A transmission is also cheaper than a life or car. Coasting downhill can create a variety of issues. Speed control, steering response (because of increased speed, reaction time, etc), and the necessity to select the proper gear when you need to. If you are pinching pennies to this point, maybe you should move on to something else. It's a dang V6 guys. At most it's a 40k-ish car. Coasting isn't worth the risk in my eyes. If you are good with accepting the risk, that is your prerogative. Fuel consumption will be minimal because you are NOT accelerating. Take it for what it is worth!

03-16-2012, 01:07 PM	#1 (permalink)
steve1ddd Base Member Join Date: Nov 2011 Location: denver Posts: 33 Drives: 09 370z touring Rep Power: 14	AT netural downhill Excuse the dumb question but i really dont know much about car engines. I have an 09 370 with Automatic Trans. I live up in the mountains and my trip down is all down hill. In my previous car which was a stick, i jsut coasted down in netural. is it bad to do this with an AT. Its about 20 miles and i dont have to put it back into gear but maybe 1 or 2 times brienfly? is there even a benifit to doing this (like saving gas?) I do notice i am able to build up more speed while not in gear and thus can coast longer. please advise.

03-16-2012, 02:09 PM	#6 (permalink)
Felix 808 A True Z Fanatic Join Date: Oct 2011 Location: Camarillo, CA Posts: 1,063 Drives: 2011 PW/Grey T/S 7AT Rep Power: 2807	Actually I am going to say it is a bad practice on a few reasons. 1. You never tow an automatic with wheels on the ground in neutral- The trans pump is not pumping vital fluid for cooling. Coasting in neutral would simulate the same conditions, causing excess heat (#1 AT destroyer). 2. Delay in power if you need to gain speed for any reason $.02 YMMV __________________ Semper Fi Μολὼν λαβέ

03-18-2012, 09:15 PM	#11 (permalink)
Jordo! A True Z Fanatic Join Date: May 2010 Location: nirvana Posts: 6,394 Drives: 2023 NATM Rep Power: 418	Throttle off in any gear, injectors are not firing. Thus, same gas mileage. So, just throttle off in gear and coast. __________________ Enjoy it. Destroy it.

03-18-2012, 10:26 PM	#12 (permalink)
roplusbee A True Z Fanatic Join Date: Dec 2009 Location: Killeen, TX Posts: 2,360 Drives: 2007 350Z NISMO Rep Power: 22	I am assuming that you can use the sport shift (or whatever they call it) to engage 3rd or 4th gear to keep a semi-constant speed while "coasting" so that you are saving brakes, keeping power at the ready, and minimizing drivetrain damage. I am not aware of how the drivetrain gets damage rolling in neutral, but the manual states that the car should not be towed in neutral. I was always taught to keep the car in gear while moving, unless you are at the point of stopping. __________________ 2007 350Z NISMO #0618: Zerolift \| UPREV \| F.I. \| Greddy \| Competition Clutch \| Injector Dynamics \| Aeromotive \| Pioneer \| JL

03-18-2012, 11:28 PM	#13 (permalink)
wilsonp A True Z Fanatic Join Date: Jul 2010 Location: Virginia Posts: 1,134 Drives: 2009 Touring Sp Nav Rep Power: 17	As Click and Clack point out, new brake pads are cheaper than a new transmission, so don't put extra wear and tear on the drivetrain for slowing down on hills. Use the parts as they are intended. __________________ 2014 Cayman S PDK Sport Chrono White/Black Was 2009 370Z Touring Sport+Nav 7AT Metallic Black/Persimmon Was 1991 NSX Auto Black/Black

03-16-2012, 01:13 PM	#2 (permalink)
harman.khinda Enthusiast Member Join Date: Feb 2012 Location: Red Bluff, CA Posts: 378 Drives: 10 Nissan 370 PG 7AT Rep Power: 6723	leave it in gear. when your coating downhill in gear their is some resistance because the wheels are driving the engine and therefore the engine is using less fuel to keep running. as opposed to putting in neutral and coasting the engine has to idle under its own power.

03-17-2012, 11:20 AM	#8 (permalink)
harman.khinda Enthusiast Member Join Date: Feb 2012 Location: Red Bluff, CA Posts: 378 Drives: 10 Nissan 370 PG 7AT Rep Power: 6723	touche'

03-17-2012, 12:45 PM	#9 (permalink)
Augustus Base Member Join Date: Jan 2012 Location: Illinois Posts: 146 Drives: 2011 370Z Touring M6 Rep Power: 13	Don't ever put a transmission in neutral when coasting downhill. Automatic or manual. Doing so is dangerous for several reasons; already mentioned above. There's also the element of brakes. In the mountains, you want to be using lower gears to maintain speeds down hills. Constant braking down a long slope is a good way to boil your brake fluid and potentially lose all braking. Never mind a lot of added wear and tear on your brake pads. I am fairly sure this is all in the owners manual. And Yes, you'll get better gas mileage with it in gear because the injectors can shut down. When idling, youre always using gas.

03-18-2012, 08:05 PM	#10 (permalink)
roy'sz A True Z Fanatic Join Date: Aug 2011 Location: palmdale, ca Posts: 1,299 Drives: 2010 nissan 370z Rep Power: 16	coasing downhill in gear does not save you gas because your rpms will be higher in gear rather than idle, if it weren't then that is one tall gear that you have. True that distance+time will decifer what you would save in fuel. If you know your rpm/gear ratio then you could match it fine, or leav it in sport mode and downshift. Obiviously that all pretty much applies to a manual. As for a automatic, if you are coasint in neutral and the car is running, you are providing transmission fluid cirulation. Not a good idea to coast though in neutral because when you put it back into drive the car has to find what gear you are in and it will most of the time start from 1st all the way to 7.

03-19-2012, 12:36 AM	#14 (permalink)
roy'sz A True Z Fanatic Join Date: Aug 2011 Location: palmdale, ca Posts: 1,299 Drives: 2010 nissan 370z Rep Power: 16	fuel pump puts out pressure to open the injectors for any type of combustion, if they aren't opening then how is it that the engine is running?

03-19-2012, 06:41 PM	#15 (permalink)
roplusbee A True Z Fanatic Join Date: Dec 2009 Location: Killeen, TX Posts: 2,360 Drives: 2007 350Z NISMO Rep Power: 22	A transmission is also cheaper than a life or car. Coasting downhill can create a variety of issues. Speed control, steering response (because of increased speed, reaction time, etc), and the necessity to select the proper gear when you need to. If you are pinching pennies to this point, maybe you should move on to something else. It's a dang V6 guys. At most it's a 40k-ish car. Coasting isn't worth the risk in my eyes. If you are good with accepting the risk, that is your prerogative. Fuel consumption will be minimal because you are NOT accelerating. Take it for what it is worth! __________________ 2007 350Z NISMO #0618: Zerolift \| UPREV \| F.I. \| Greddy \| Competition Clutch \| Injector Dynamics \| Aeromotive \| Pioneer \| JL