Coasting in Neutral, Automatic Transmission

[Red1]

Hi Guys,

I've heard that on a long flat (or downhill) slope, you can save on fuel economy by shifting into neutral. I've tried it just a few times, and it seems that way. You can feel the difference too, because (at least it seems this way) in drive, you feel the engine "pulling you down" - ie, slowing you down more than the natural coasting speed. The times I've done it I shift into N while driving, but don't shift back into drive untill I am at a complete stop (such as coming up on a stop sign or red light).

Does that hurt the transmission, gears, or engine in any way? I remember reading something in the owner's manual about "not advising" a shift while moving, but I was assuming that's only shifting from N INTO D while traveling (since you can shift into neutral without even pushing in the button). Or maybe, even is both ways OK? And, does it save on fuel economy?

I'm not too mechanically minded, so I would appreciate hearing any and all opinions and facts. thanks!

[jayman]

i do it all the time and it does let you coast further, not sure it it hurts the tranny but it hasn't affected mine

[thehunterooo]

I do the same sometimes, we were never able to figure out if it had a negative effect on the transmission though. From 1 to 2, it allows you to shift into it without the button being pressed. Then 2 to D4 and finally D4 to N is the same. Downshifting from D4 to 2 and 2 to 1 does require the button being pressed though (I only have downshifted to test and such). About 40,000 miles (55,000 total) on the car and no issues, my transmission shifts beautifully. But you never know...

[gone.m]

My mechanic told me when I asked him that this does not harm the transmission. He is a certified GM mechanic with 8+ years experience. He is also my best friend and just stood up as best man in my wedding, so I know he's not lying.

You sound like someone who would be interested in hypermiling. Cleanmpg.com is a great resource for this driving technique. You can find the technique you described and dozens more on that site. Oh, and I've been utilizing the coasting technique, plus when I'm coasting I shut the engine off. It's called forced-auto stop and it saves a ton of gas since while you're coasting with the engine off, you are getting infinite miles per gallon

[gclark8]

This article may help: Coasting in Neutral or Gear to Save Gas - Coasting and Fuel Economy - Popular Mechanics

[gone.m]

This article may help: Coasting in Neutral or Gear to Save Gas - Coasting and Fuel Economy - Popular Mechanics

The article can't be absolutely true. If it was, then how do I average 35.5 mpg in my 04 Aveo using said techniques in over 90% city driving? The EPA estimates an average of 26 mpg.

To qualify that, I should mention that I only coast to minimize slamming on the brakes coming up to a stop sign or red light. If you use the coasting and slow acceleration to keep the car constantly rolling instead of starting and stopping frequently, your gas mileage will improve significantly. That is a no brainer.

If you feel it is an unsafe technique, then by all means do not use it. But it is needless and untruthful to argue that it doesn't save gas. It does. If you don't believe it, go here: CleanMPG, An authoritative source on fuel economy and hypermiling and here: Fuel Economy, Hypermiling, EcoModding News and Forum - Ecomodder.com Fuel Economy Forum, research the issue, then come back and tell me your findings.

Here is a rebuttal to AAA's findings that such techniques are unsafe: CleanMPG, - AAA Response An authoritative source on fuel economy and hypermiling

[Thymeclock]

The article can't be absolutely true. If it was, then how do I average 35.5 mpg in my 04 Aveo using said techniques in over 90% city driving? The EPA estimates an average of 26 mpg.

To qualify that, I should mention that I only coast to minimize slamming on the brakes coming up to a stop sign or red light. If you use the coasting and slow acceleration to keep the car constantly rolling instead of starting and stopping frequently, your gas mileage will improve significantly. That is a no brainer.

If you feel it is an unsafe technique, then by all means do not use it. But it is needless and untruthful to argue that it doesn't save gas. It does. If you don't believe it, go here: CleanMPG, An authoritative source on fuel economy and hypermiling and here: Fuel Economy, Hypermiling, EcoModding News and Forum - Ecomodder.com Fuel Economy Forum, research the issue, then come back and tell me your findings.

Here is a rebuttal to AAA's findings that such techniques are unsafe: CleanMPG, - AAA Response An authoritative source on fuel economy and hypermiling

I'm not concerned with the driving technique of coasting in neutral being unsafe. I'm concerned with potential damage to the A/T.

If you take the A/T out of drive and coast with it in neutral to a stop or an almost stop, there will be no problem. That is known to be OK. However, if you do the same at a high speed (above let's say 60 MPH) and re-engage it back into drive at a speed above 50 MPH: the transmission will want to enter fourth gear and it is also programmed to be running with the torque converter engaged at speeds above 45 MPH.

What do you think will happen to the torque converter? Are you willing to risk damaging it, possibly incurring a very high repair bill, for the sake of saving a few cents on fuel?

[petrified.rabbit]

gclark ive said that time and time again, but have been told on here that the aveo does not cut fuel on coast/deceleration.

i guess i need to get the scan tool out and check once its back on the road.

[FASTRAKR]

I just recieved my Ultragauge EM two days ago and I am still learning it, but I know it will tell me if there is fuel cut or not. I just have to figure out where it tells me.

BTW, the new Ultra-gauge EM is pretty cool. I am Beta testing it for them and they have added a few gauges plus it does metric for us Northerners.

[Red1]

I read the Popular Mechanics article and the responses. Really seems like a contentious issue! How can an average Joe like me know?

I do know for sure that my Aveo's engine "keeps going" while in drive as I coast down a long freeway offramp everyday. I don't know the exact term, but if I leave it in drive it pulls the car down, and I have to give it some gas just a touch longer to get there. In neutral, it maintains a higher speed. I suppose that's why it seems like you would save on fuel, but again, I'm not a mechanic. My old Ford Taurus didn't "engine brake" nearly as much, and coasting felt more free-rolling.

Is that unique to the Aveo, or am I still just adjusting? Someone put something above about Aveo not "cutting fuel" on deceleration - but I don't know what that means. Can anyone explain?

On the positive side, my last fill up (second ever in this car) was just over 30 mpg (about 65% highway, and I'm trying to be very careful about trying to stick around max. 55-65 mph). Not going to win any awards, but considering I was averaging 20-21 mpg in my Taurus, I'm happy!