Are my habits harmful to this CVT?

Posted by: gr8gatzby

Are my habits harmful to this CVT? - 12/09/13 11:13 PM

My mother drives a 2012 Murano with a super sweet CVT. I've never met a CVT I liked, so for me to say this surprises me. Prior to this she drove a 2004 Murano with a [censored] arse piece-o-garbage how-i-loathed-thee CVT. The mannerisms and personality between these two are night and day, and I am amazed how much can change in a generation.

There is a single negative characteristic that has carried over to the current Nissan CVT: it will not "downshift" when going down hills. For example, I'm travelling 70mph at 2k rpm and approach a 1mi decline, revs stay at 2k rpm for the downward run. Being the engineer nerd that I am, I throw the gearbox to neutral to save this wasted energy and add the extra .0000001 miles to the tank of gas.

A regular geared automatic will drop to near-idle revs when the energy is not needed on a downhill slope. On my stick shift Volvo I drop it in neutral as well.

I am curious, is this shifting to and from neutral at speed doing any long term harm to the transmission? Can my OCD regarding wasted energy be justified? Thanks.
Posted by: Rand

Re: Are my habits harmful to this CVT? - 12/09/13 11:14 PM

you will actually use more gas by putting it in neutral.
Posted by: gr8gatzby

Re: Are my habits harmful to this CVT? - 12/09/13 11:18 PM

How so? 500rpm vs 2000rpm over 1 mile = less gas.
Posted by: Shannow

Re: Are my habits harmful to this CVT? - 12/09/13 11:20 PM

You are, in all likelihood running fuel cut-off on downhill...dropping it into neutral, the engine will be idling, and using fuel.

You will also have some additional load on the brakes which will be costing you money over time (cents likely).
Posted by: JHZR2

Re: Are my habits harmful to this CVT? - 12/09/13 11:21 PM

Originally Posted By: Rand
you will actually use more gas by putting it in neutral.



Thats arguable. In theory, yes, you will because the PWM on the injectors will be re-enabled to maintain idle, as opposed to turned off when closed throttle coasting in gear.

However, if at the end of the slope maximum momentum is required, going in neutral will save the pumping losses which effectively act as a brake.

My concern in any AT type vehicle is that the transmission may not be circulating lubricant properly if the pump is on the input shaft, thus causing increased wear. IIRC, only AT vehicles with a pump on the output side can be suitably pulled/coasted without potential for damage.
Posted by: gregk24

Re: Are my habits harmful to this CVT? - 12/09/13 11:27 PM

Doing more harm than good.
Posted by: daves87rs

Re: Are my habits harmful to this CVT? - 12/09/13 11:49 PM

Honestly can't see it helping much....
Posted by: CHARLIEBRONSON21

Re: Are my habits harmful to this CVT? - 12/09/13 11:55 PM

No "L" slot? My fusion has that...
Posted by: actionstan

Re: Are my habits harmful to this CVT? - 12/09/13 11:58 PM

Originally Posted By: gr8gatzby
How so? 500rpm vs 2000rpm over 1 mile = less gas.


RPM isn't always equal to fuel usage. The computer will call for less fuel usage when rolling down a hill, as there is less strain on the engine. I feel like this is doing more harm than good, and you are better off staying in gear 100% of the time, until you are parking the car.
Posted by: bvance554

Re: Are my habits harmful to this CVT? - 12/10/13 12:02 AM

Originally Posted By: JHZR2
Originally Posted By: Rand
you will actually use more gas by putting it in neutral.



Thats arguable. In theory, yes, you will because the PWM on the injectors will be re-enabled to maintain idle, as opposed to turned off when closed throttle coasting in gear.

However, if at the end of the slope maximum momentum is required, going in neutral will save the pumping losses which effectively act as a brake.

My concern in any AT type vehicle is that the transmission may not be circulating lubricant properly if the pump is on the input shaft, thus causing increased wear. IIRC, only AT vehicles with a pump on the output side can be suitably pulled/coasted without potential for damage.


Its not arguable. Leaving it in gear and coasting you will use zero gas, versus coasting neutral and using a minimal amount of gas. Given that, there is absolutely no reason to coast down hill in neutral. Maybe even a little dumb and unsafe.
Posted by: Shannow

Re: Are my habits harmful to this CVT? - 12/10/13 12:09 AM

Originally Posted By: JHZR2
My concern in any AT type vehicle is that the transmission may not be circulating lubricant properly if the pump is on the input shaft, thus causing increased wear. IIRC, only AT vehicles with a pump on the output side can be suitably pulled/coasted without potential for damage.


Been through that in my head with the 4L60E in my caprice.

In neutral and idling, the pump is still pumping. On over-run, the power flow might be reversed, but the pump is still spinning and pumping normally...even with the ignition off (or a dead fuel pump), as long as you were coming from an operational state in drive, the pump is still turning and pumping.

All scenarios are different from rolling it down a hill with the engine off from the start.

Only ever seen a couple of powerglides and an old humber that could be push started.
Posted by: gr8gatzby

Re: Are my habits harmful to this CVT? - 12/10/13 12:09 AM

Quote:
Maybe even a little dumb and unsafe.


I agree that it is dumb and unsafe. That is not my quandary.

If I am doing no harm to the CVT by shifting to and from neutral while in motion in an effort to prevent unnecessary revs to the engine, and willing to accept the risks to the safety of myself and my passengers, why not do it?
Posted by: Shannow

Re: Are my habits harmful to this CVT? - 12/10/13 12:10 AM

Because you get a $180 ticket if the cop thinks you are coasting in neutral (in either an auto or manual) in my state.
Posted by: gr8gatzby

Re: Are my habits harmful to this CVT? - 12/10/13 12:11 AM

Originally Posted By: Shannow
Because you get a $180 ticket if the cop thinks you are coasting in neutral (in either an auto or manual) in my state.


You live in the state of North Korea?
Posted by: Kuato

Re: Are my habits harmful to this CVT? - 12/10/13 12:15 AM

Originally Posted By: Shannow
Because you get a $180 ticket if the cop thinks you are coasting in neutral (in either an auto or manual) in my state.


It's illegal lots of places in the US also.

/hijack
Posted by: actionstan

Re: Are my habits harmful to this CVT? - 12/10/13 12:19 AM

Originally Posted By: gr8gatzby
Quote:
Maybe even a little dumb and unsafe.


I agree that it is dumb and unsafe. That is not my quandary.

If I am doing no harm to the CVT by shifting to and from neutral while in motion in an effort to prevent unnecessary revs to the engine, and willing to accept the risks to the safety of myself and my passengers, why not do it?


It may not damage anything, but you win nothing by doing it. I think you should go back and read the last part, that just sounds ludicrous..safety among all else should be the #1 priority of whoever is in the driver seat. When rolling while in gear, fuel cutoff happens, to either completely cut, or minimize fuel usage. What are you trying to gain here?
Posted by: gathermewool

Re: Are my habits harmful to this CVT? - 12/10/13 12:30 AM

Originally Posted By: gr8gatzby
Quote:
Maybe even a little dumb and unsafe.


I agree that it is dumb and unsafe. That is not my quandary.

If I am doing no harm to the CVT by shifting to and from neutral while in motion in an effort to prevent unnecessary revs to the engine, and willing to accept the risks to the safety of myself and my passengers, why not do it?


1. Have you read the posts stating that:

a. The injectors shut off in many autos while engine-braking downhill;

b. The engine is braking, so you don't need to use your actual brakes to maintain downhill speed;

c. If an emergency arises, you have the vehicle in gear to provide acceleration.

2. Read what you typed and ask yourself if it makes any sense at all...
Posted by: gr8gatzby

Re: Are my habits harmful to this CVT? - 12/10/13 12:46 AM

Quote:
a. The injectors shut off in many autos while engine-braking downhill;


Engine braking is not a factor when revving at idle speeds

Quote:
b. The engine is braking, so you don't need to use your actual brakes to maintain downhill speed;


Engine braking should only be used as a method of deceleration in emergencies. Engines are more expensive to replace than brake pads.

Quote:
c. If an emergency arises, you have the vehicle in gear to provide acceleration.


I agree, that's why I only shift into neutral on a downslope when not surrounded by traffic, and risk is at an absolute minimum.
Posted by: Dominic

Re: Are my habits harmful to this CVT? - 12/10/13 01:28 AM

Bad idea, leave it in gear - it will use less fuel with the injectors "off" and the car momentum spinning the engine than if the engine is forced to idle on its own.
Posted by: demarpaint

Re: Are my habits harmful to this CVT? - 12/10/13 01:39 AM

Originally Posted By: Kuato
Originally Posted By: Shannow
Because you get a $180 ticket if the cop thinks you are coasting in neutral (in either an auto or manual) in my state.


It's illegal lots of places in the US also.

/hijack


+1
Posted by: PandaBear

Re: Are my habits harmful to this CVT? - 12/10/13 01:47 AM

Just out of curiosity, when did car engine start using fuel cutoff during deceleration or going downhill to save gas? Was it when they started using fuel injectors? or only when they start using computer intensively?
Posted by: 901Memphis

Re: Are my habits harmful to this CVT? - 12/10/13 01:53 AM

Originally Posted By: PandaBear
Just out of curiosity, when did car engine start using fuel cutoff during deceleration or going downhill to save gas? Was it when they started using fuel injectors? or only when they start using computer intensively?


OBD2 iirc
Posted by: Shannow

Re: Are my habits harmful to this CVT? - 12/10/13 01:53 AM

http://www.auto-tat.co.uk/Escort%20Upgrades/Chapters/Engine/CVH/Bosch%20K-Jetronic.htm

Fair while ago
Posted by: Tegger

Re: Are my habits harmful to this CVT? - 12/10/13 03:14 AM

Originally Posted By: 901Memphis
Originally Posted By: PandaBear
Just out of curiosity, when did car engine start using fuel cutoff during deceleration or going downhill to save gas? Was it when they started using fuel injectors? or only when they start using computer intensively?

OBD2 iirc

Well before that. My '91 Integra shut off the fuel on decel above something like 1,500 rpm.

The shutoff limit has been lowered over the years as engine computers have gotten faster and emissions regulations tighter. I think the newest cars shut off fuel on decel just above idle speed.

My understanding is that fuel-cutoff on decel wasn't practical before electronic injection.
Posted by: Voltmaster

Re: Are my habits harmful to this CVT? - 12/10/13 05:05 AM

i used to use neutral as much as possible on my Accord, after my tranny failure i decided to just put it at d4 and let it be.

I have not noticed any mpg gains or losses, engine will never rev down to below 500 rmp to your save basicly nothing.
Posted by: eljefino

Re: Are my habits harmful to this CVT? - 12/10/13 05:21 AM

You've made up your mind! Go for it.

Also take note when you put it back in drive it has to rev-match somehow, which is different than you doing so when stationary.

Originally Posted By: gr8gatzby
Quote:
a. The injectors shut off in many autos while engine-braking downhill;


Engine braking is not a factor when revving at idle speeds

Posted by: fdcg27

Re: Are my habits harmful to this CVT? - 12/10/13 05:53 AM

Our old Mercedes four apeed automatics had instructions in the OMs for tow starting them.
You had to be going at a decent clip, though.
It isn't like push starting a stick.
Posted by: Pop_Rivit

Re: Are my habits harmful to this CVT? - 12/10/13 06:27 AM

Originally Posted By: gr8gatzby
I agree that it is dumb and unsafe. That is not my quandary.


It should be. You have a responsibility to your fellow motorists as well as your passengers to operate your vehicle in the safest possible manner. If, by your own admission it's both "dumb and unsafe" then the conversation ends there. Don't do it. There are a lot of people here telling you just how dumb and unsafe it is, but you're refusing to listen.
Posted by: Char Baby

Re: Are my habits harmful to this CVT? - 12/10/13 07:20 AM

Slightly off topic...Though this only pertains to regular auto trannys(for those who want to know), IDK how this in particular relates to CVT's:

In a regular automatic tranny, by putting the gear selector in "N" while coasting as compared to keeping it in "D", the trannys torque converter is spinning at a higher speed and the engine is now at idle. Where as they(engine speed/tranny tq conv) should both be at the same speed while coasting/foot off the gas pedal at speeds.

I too have done this(gear selector in "N") on numerous occassions w/o issues but, it's probably not optimal!

Did I say all of this correctly?
Posted by: Charlie1935

Re: Are my habits harmful to this CVT? - 12/10/13 07:21 AM

Been illegal in Illinois for a long time.
Posted by: The_Eric

Re: Are my habits harmful to this CVT? - 12/10/13 07:30 AM

Originally Posted By: gr8gatzby
Quote:
a. The injectors shut off in many autos while engine-braking downhill;


Engine braking is not a factor when revving at idle speeds

Quote:
b. The engine is braking, so you don't need to use your actual brakes to maintain downhill speed;


Engine braking should only be used as a method of deceleration in emergencies. Engines are more expensive to replace than brake pads.

Quote:
c. If an emergency arises, you have the vehicle in gear to provide acceleration.


I agree, that's why I only shift into neutral on a downslope when not surrounded by traffic, and risk is at an absolute minimum.


I think it's already been established that you're not gaining anything to take it out of gear while coasting and if you think that you are going to wear an engine out coasting down some random hill at 2000 rpm, then you have some pretty serious misconceptions about engines. That engine will be completely fine and more than likely outlast the car, barring some fluke failure. Stop worrying and splitting hairs, life is too short for trivial things like this and it won't gain you anything that you be able to quantify anyway.
Posted by: demarpaint

Re: Are my habits harmful to this CVT? - 12/10/13 07:34 AM

Originally Posted By: The_Eric

I think it's already been established that you're not gaining anything to take it out of gear while coasting and if you think that you are going to wear an engine out coasting down some random hill at 2000 rpm, then you have some pretty serious misconceptions about engines. That engine will be completely fine and more than likely outlast the car, barring some fluke failure. Stop worrying and splitting hairs, life is too short for trivial things like this and it won't gain you anything that you be able to quantify anyway.


A little engine breaking is actually good for the engine. It can help keep the rings free from sticking.
Posted by: dparm

Re: Are my habits harmful to this CVT? - 12/10/13 08:32 AM

Unsafe to put it in neutral, actually. If you need to take evasive action, you don't want the car out of gear. Also puts unnecessary wear and tear on the trans.
Posted by: bigjl

Re: Are my habits harmful to this CVT? - 12/10/13 08:55 AM

Originally Posted By: gr8gatzby
Quote:
a. The injectors shut off in many autos while engine-braking downhill;


Engine braking is not a factor when revving at idle speeds

Quote:
b. The engine is braking, so you don't need to use your actual brakes to maintain downhill speed;


Engine braking should only be used as a method of deceleration in emergencies. Engines are more expensive to replace than brake pads.

Quote:
c. If an emergency arises, you have the vehicle in gear to provide acceleration.


I agree, that's why I only shift into neutral on a downslope when not surrounded by traffic, and risk is at an absolute minimum.


Did you say you were an engineer?

I know nobody that would do as you suggest or even consider it a sensible course of action

The vehicle was engineered to run as it does when coasting down a hill

That is why it does it.

Or are you saying the engineers involved don't know what they are doing?
Posted by: supton

Re: Are my habits harmful to this CVT? - 12/10/13 09:00 AM

DBW, right? In engine over-run it likely isn't injecting any fuel, and it's possible that it's not pulling air over a closed throttle plate either. If it feels like it coasts without dragging then I'm not sure I'd worry about it.
Posted by: gr8gatzby

Re: Are my habits harmful to this CVT? - 12/10/13 09:01 AM

Originally Posted By: bigjl
Originally Posted By: gr8gatzby
Quote:
a. The injectors shut off in many autos while engine-braking downhill;


Engine braking is not a factor when revving at idle speeds

Quote:
b. The engine is braking, so you don't need to use your actual brakes to maintain downhill speed;


Engine braking should only be used as a method of deceleration in emergencies. Engines are more expensive to replace than brake pads.

Quote:
c. If an emergency arises, you have the vehicle in gear to provide acceleration.


I agree, that's why I only shift into neutral on a downslope when not surrounded by traffic, and risk is at an absolute minimum.


Did you say you were an engineer?

I know nobody that would do as you suggest or even consider it a sensible course of action

The vehicle was engineered to run as it does when coasting down a hill

That is why it does it.

Or are you saying the engineers involved don't know what they are doing?


I am saying the transmission is inherently flawed if it revs at 2k rpm when on a downward slope. As to whether the engineers know what they are doing is anyone's guess. I've seen this behavior in other CVTs, so I assume that it is an engineering obstacle inherent to the CVT design that has yet to be overcome.
Posted by: mcrn

Re: Are my habits harmful to this CVT? - 12/10/13 09:36 AM

Doesn't this put more wear on the transmission and possibly engine mounts?
Posted by: Rolla07

Re: Are my habits harmful to this CVT? - 12/10/13 10:17 AM

Id figure there is no true benefit to it. If your foot is off the gas pedal, I doubt there is much difference whether its in neutral or drive. So why bother doing it?
Posted by: gathermewool

Re: Are my habits harmful to this CVT? - 12/10/13 10:46 AM

Originally Posted By: gr8gatzby
Quote:
a. The injectors shut off in many autos while engine-braking downhill;


Engine braking is not a factor when revving at idle speeds

Quote:
b. The engine is braking, so you don't need to use your actual brakes to maintain downhill speed;


Engine braking should only be used as a method of deceleration in emergencies. Engines are more expensive to replace than brake pads.

Quote:
c. If an emergency arises, you have the vehicle in gear to provide acceleration.


I agree, that's why I only shift into neutral on a downslope when not surrounded by traffic, and risk is at an absolute minimum.


a. Exactly, so why idle at 0.3 gph fuel burn rate when you can engine-brake at 0.000000 gph? I don't get your logic.

b. Engine braking should be used as often as possible; it does no harm to your engine, and the high vacuum is usually seen as helpful during break-in.

c. See above comments
Posted by: Vikas

Re: Are my habits harmful to this CVT? - 12/10/13 10:51 AM

Originally Posted By: eljefino
You've made up your mind! Go for it.
why don't other participants here understand this simple concept? I believe I am the one who owns the patent on this though :-)
Posted by: gathermewool

Re: Are my habits harmful to this CVT? - 12/10/13 10:52 AM

Also, engine braking often is how I was able to get mixed to highway mpg in my previous vehicle, a WRX STI. Every night after work, I keep it in second gear, rev up to 3k RPM and coast down the hill until I turn into my condo complex; I do the same when coming off the bridge that ends on a big downhill, off-ramp, and an always-red stop light (I rev-match and shift to third and engine-brake for a good 30 seconds) These are only minor examples, but for the time that I'm engine-braking, I'm burning zero fuel.
Posted by: JTK

Re: Are my habits harmful to this CVT? - 12/10/13 11:01 AM

I really like ATs with grade-logic. It should only come into play when accelerating with your foot off the go-pedal and a lot of them will disable if they have a "sport mode" button. My 2002 Isuzu Rodeo had this (4L30E trans) and my 2008 Honda Odyssey had it. IIRC, the Ody would only kick down if you were picking up speed on the down-hill and apply the brakes.

FWIW, the CVT drivetrain on my 2012 Subaru Legacy offers noticeable compression braking when you let off the gas. I like it.

OTOH, the 6spd in our new Dodge Grand Caravan will coast on forever. No slowing down unless you brake.
Posted by: Kuato

Re: Are my habits harmful to this CVT? - 12/10/13 11:36 AM

Wait, this is your Mom's car, right? If she doesn't care (or even notice!) then no worries.

And since you hate cvt transmissions, avoid driving and all is well.
Posted by: CBR.worm

Re: Are my habits harmful to this CVT? - 12/10/13 01:41 PM

BTW, assuming your mom lives in the same state that you do, it is illegal to coast there as well. I got a ticket coasting down a hill in NC (with a manual tranny). I don't remember the exact wording of the ticket - it was pretty vague but apparently illegal.
Posted by: gr8gatzby

Re: Are my habits harmful to this CVT? - 12/10/13 01:50 PM

You got a ticket for speeding, or for coasting in neutral? How would a cop know if a vehicle is in neutral in either transmission?
Posted by: TFB1

Re: Are my habits harmful to this CVT? - 12/10/13 02:06 PM

If there is enough of a down hill grade that speed is increasing, I'll down shift and use engine braking, no fuel used and brakes aren't going to possibly overheat...

The thought of wearing out engine by downshifting is basically B-S...
Posted by: Shannow

Re: Are my habits harmful to this CVT? - 12/10/13 04:57 PM

Originally Posted By: gr8gatzby
Engine braking should only be used as a method of deceleration in emergencies. Engines are more expensive to replace than brake pads.



Originally Posted By: gr8gatzby
I am saying the transmission is inherently flawed if it revs at 2k rpm when on a downward slope. As to whether the engineers know what they are doing is anyone's guess. I've seen this behavior in other CVTs, so I assume that it is an engineering obstacle inherent to the CVT design that has yet to be overcome.


As an engineer myself, I'm very very interested in how you've come to these views...

If in a manual, running down a hill, the engine is turning at the same speed as if you were going up the hill...how can that be damaging, or a design flaw if the CVT behaves the same ?
Posted by: CBR.worm

Re: Are my habits harmful to this CVT? - 12/11/13 06:18 PM

[quote=gr8gatzby]You got a ticket for speeding, or for coasting in neutral? How would a cop know if a vehicle is in neutral in either transmission?[/quote

For coasting in neutral. I don't know how he knew, but he was right. I was from out of state and didn't want any problems so I didn't argue.
Posted by: Artem

Re: Are my habits harmful to this CVT? - 12/11/13 06:28 PM

Originally Posted By: gr8gatzby


I am saying the transmission is inherently flawed if it revs at 2k rpm when on a downward slope. As to whether the engineers know what they are doing is anyone's guess. I've seen this behavior in other CVTs, so I assume that it is an engineering obstacle inherent to the CVT design that has yet to be overcome.


My 2011 Avalon will keep the same engine speed if I'm on the highway doing 75mph and let go of the gas pedal to coast for a bit when going downhill.

It would cause extra wear and tear if it disengages the gear every time to took your foot off the gas pedal for the slightest amount and reapplied.

The MPG gauge shows 99.9mpg when coasting in gear.

OP, you need to get a scan gauge and re-evaluate your driving style because it's FLAWED.