Shifting into neutral

[otterhere]

Does doing this at stoplights really help mpg on an automatic transmission, or is that just a myth? We have a difference of opinion on it among my friends.

[lita_g]

From what I've been reading here and asking around, it's supposed to, but I was also told that it may affect your transmission in the long run, so I won't risk saving a few cents in gas and then having to spend more fixing my transmission.

[BailOut]

It does save gas because it decreases drag on the engine but it is nowhere near as efficient as just turning off the engine.

The wear on the transmission from going between N and D is negligible, and represents much less forces than even moderate acceleration. Prior to the mid 1990's some American makes did indeed have issues with frequent manual gear selections on an AT, and one South Korean manufacturer still does (Daewoo, makers of the Chevy Aveo), but it is nothing to worry about in the Yaris.

[Mikeb Yaris]

Otter,

You asked a couple questions before the other thread was closed.

Re: Tire inflation vs snow - We don't get much snow here, so I don't know how inflating to max will effect handling. We did have some sleet last night and I couldn't tell that the car handled poorly.

Re: Speed @ 1100 rpm - this is inexact of course, but decellerating after being in OD, I put 1100 rpm at just between 30 and 35 mph.

[BailOut]

High tire pressure on the snow is actually better than lower pressure, unless you go very low, say to 5-7 PSI. With any amount of air in the tires maintaining traction is all about moving water, snow, mud, etc. out of the way, so higher pressure is better as it holds the tire's shape better, allowing it to more effectively eject snow from the tread.

I run my tires at 60 PSI. I drove us to and from work over the mountain for the last two days while a storm was dumping 2 feet of snow. I have yet to put my spikes spiders on.

[thebarber]

Originally Posted by BailOut

It does save gas because it decreases drag on the engine but it is nowhere near as efficient as just turning off the engine.

The wear on the transmission from going between N and D is negligible, and represents much less forces than even moderate acceleration. Prior to the mid 1990's some American makes did indeed have issues with frequent manual gear selections on an AT, and one South Korean manufacturer still does (Daewoo, makers of the Chevy Aveo), but it is nothing to worry about in the Yaris.

so youre saying i shouldnt shift into neutral in my ATX aveo? lol

[BailOut]

Originally Posted by thebarber

so youre saying i shouldnt shift into neutral in my ATX aveo? lol

I would not do it often. I was "educated" by the GM dealership my rental Aveo was serviced at after I threw a CEL for using neutral like that. Let's just say that they are not fans of the transmission used in the Aveo.

[Reddog99]

Originally Posted by otterhere

Does doing this at stoplights really help mpg on an automatic transmission, or is that just a myth? We have a difference of opinion on it among my friends.

Does it save gas? Sometimes, but very, very little...

I've watched the TPS (Throttle Position Sensor) on my Scangage and it will normally idle with a value of 15 when in neutral. When in gear, it will idle at 16-17 until everything is good and hot (20-30 minutes running). After that, it will settle down to 15 while idling in gear. Unless you did an awful lot of idling in gear, I doubt that you would be able to even see the difference in your mileage at fill-up time.

As BailOut pointed out, shutting off the engine is much more efficient. You can't beat no gas use at all! Of course, then you'll start wondering if you're wearing out your starter.

[voodoo22]

From my experience Bailout is right, like usual. I drive an auto.

The general rules I abide by are to turn off the car when idling for longer than 7 seconds and I can safely turn the car back on and get going without annoying traffic behind me by making them wait for me to shift the car into D after starting.

Higher psi will give you better handling in winter. I'm up to 56 psi on my winters now and this morning saw very bad conditions. The grip is better and so is everything else except for ride comfort.

[Mikeb Yaris]

Of course, ride comfort IS and issue and there is no REAL right or wrong here. Think it's too firm for your behind at 40psi? Then by all means run it as low as 32!

FOR ME, 44 feels just fine. I might someday try as high as 50, but I'm in no rush. I don't judge the over-inflators, but I likewise don't judge the normal inflators - until they fail to recognize two undeniable facts:

1) Car companies want you to marvel over their great ride and will do things to enhance that (I found my car inflated to under 30 from the dealer)

2) Tort - this is why your hair dryer cautions you not to use it in the shower and preparation H cautions not to use it orally

If you recognize those two things, I can respect any preference for tire inflation.

[MadMax]

If you are only seeking higher gas mileage, then by all means inflate your tires as much as you can and/or want.

But understand that this is a tradeoff and a compromise, that you do lose grip/traction and that the tire wear will be greater in the center of the tread...and as mentioned, the ride will be a lot harsher.

There is no perfect solution here, just what works for each individual.

[voodoo22]

Originally Posted by MadMax

If you are only seeking higher gas mileage, then by all means inflate your tires as much as you can and/or want.

But understand that this is a tradeoff and a compromise, that you do lose grip/traction and that the tire wear will be greater in the center of the tread...and as mentioned, the ride will be a lot harsher.

There is no perfect solution here, just what works for each individual.

I agree you need to do what you are comfortable with and everyone is different, but the only compromise of inflating your tires to max sidewall over the suggested psi from your car manufacturer is ride comfort. The other downsides you list are false.

[thebarber]

Originally Posted by voodoo22

I agree you need to do what you are comfortable with and everyone is different, but the only compromise of inflating your tires to max sidewall over the suggested psi from your car manufacturer is ride comfort. The other downsides you list are false.

can you load up your car the same (w/ ppl and a full trunk, say?) or what about for towing (assuming a 1000lbs w/ trailer and junk)?

[MadMax]

Originally Posted by voodoo22

I agree you need to do what you are comfortable with and everyone is different, but the only compromise of inflating your tires to max sidewall over the suggested psi from your car manufacturer is ride comfort. The other downsides you list are false.

Sorry, I disagree. An overinflated tire does not grip/provide traction as well as one that has lower pressure...but most hypermilers don't realize that as they accelerate/deccelerate/travel at much slower rates than most folks...

[GeneW]

Originally Posted by otterhere

Does doing this at stoplights really help mpg on an automatic transmission, or is that just a myth? We have a difference of opinion on it among my friends.

My Scangage shows such a tiny gain that it's not worth the bother. I think that the Yaris actually adjusts for the tranny when it's idling. Then there is the "I forgot to shift it back into drive and got the motor to over rev" situation.

Far better strategery is to shut off the motor if you expect to wait longer than seven seconds AND you feel that you don't need to have to be able to run away in a hurry. There are times that you must be vigilant against drunks and hooligans on the road and thus you're better off idling. Other times, like on Sunday afternoon at a long light, it does help to shut off the motor.

Gene

[GeneW]

Originally Posted by BailOut

I would not do it often. I was "educated" by the GM dealership my rental Aveo was serviced at after I threw a CEL for using neutral like that. Let's just say that they are not fans of the transmission used in the Aveo.

GM in my experience has this tendency to slap something together sometimes, especially their drive train components, and more so lately.

The Turbo 400 and to a lesser degree Turbo 350 were legends. The Powerglide is still being made today for race use. Once upon a time GM got it right and kept it going right.

I drove cars with 700R4 and 200R4 and 250C transmissions, which were what GM made when they had to lighten things up to make fuel efficiency CAFE standards or just to keep the doors open in the factories.

The 200R4 is a small sized unit that is used in medium to small cars, where it works well. Put one in behemoth like a Pontiac Parisienne and you're asking for trouble. I got 108,000 out of mine and was told, "That's pretty damn good for one of those piece of sh-t". The Pro added that most die at less than 100K miles. That's not too comforting.

I've been told by Pros that they're okay if you set them up properly, but such a thing isn't possible in an assembly line environment. A lot of old timers used to rip them out and replace them with Turbo 350s which hammer your gas mileage but are far more durable than the 200R4. Which begs the question why GM didn't just a Turbo 350 to give their customers durable cars? Well, silly me, they have to make CAFE regs and keep their processes stable.

Drove a Caprice with a 700R4. They are well regarded if you build them "right" but they have some odd habits. The "hunting" thing - the car will literally switch back and forth between third gear and overdrive around the transition speed (roughly 52 to 57 mph depending upon engine load) if you leave the selector in OD. This is because OD drops the load on the motor, which adjusts RPM down to 2000 RPM, which is a fine rate for efficiency. Because the transition speed is a borderline condition it sets up an oscillation between OD and 3rd gear, with the motor surging up and down while making the car slightly surge forwards and backwards.

While it's hunting the car makes this odd "tugging" sensation while the motor revs up and down going between OD and 3rd gear. The car sounds and feels like it's having sexual intercourse - surging forwards and backwards while softly moaning with engine noise changes. GM did this to increase its gasoline mileage but the only cure for a consumer to deal with "hunting" is to keep the gear selector in "3" which hammers your mileage.

The primitive computer used in pre OBD-II models cannot cope with this "hunting" but there are aftermarket gadgets to make it stop. There are some very small and weak gears used for the OD in production models, which can be easily damaged by normal use. The tranny was a good idea with a poor execution. I have friends who use them in souped up cars and they routinely will blow up rear ends with them. Do it right and they're tough, but GM doesn't routinely do it right.

Then we have the 250C.... oddest tranny I ever encountered. GM made it similar to a Turbo 350 but lightened up the internal parts to reduce rotary inertia. That's cool. What isn't cool is that the pump is either under powered or the unit has some odd galleries or other aspects. When you first start it up and put it into "D" you have to wait about three seconds before it will move. Stepping on the gas will damage it. Good friend of mine whose father worked as a professional mechanic had one and loved it, but cautioned me never to "step on it" to make it go before the pump pressure reached proper levels. "You'll blow it up" he said.

I'm not surprised that the Aveo is touchy about its tranny. The Ford Escort of the 1990s had three sensors in it to monitor tranny use. If any of them failed the tranny would rapidly self destruct. Engineers do the oddest things sometimes to save a buck here and there.... I can only imagine what Daewoo did under the guidance of the MBA Corps at GM HQ.

GM, Mark of Excellence..... Yeah, right.

Gene

[YenOfIrrelevent]

So it will be safe for a Yaris sedan to switch into neutral right? I have been doing it for the past two weeks and nothing happened yet but if there is something I should know that may occur please reply. Thanks.

[BailOut]

Originally Posted by YenOfIrrelevent

So it will be safe for a Yaris sedan to switch into neutral right? I have been doing it for the past two weeks and nothing happened yet but if there is something I should know that may occur please reply. Thanks.

You will be just fine as long as you leave the engine running while coasting in neutral.