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Old 07-15-2011, 08:49 PM   #1
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Automatics and Engine On Coasting...

Does anyone do coasting (engine on) in their automatic?

Is there a down side to it? (bad on transmission, engine, whatever).

Currently looking into a fiero. It will be automatic. But for daily driver purposes, I may want to drive to work for as little as possible.
Automatic okay for neutral coasting? Or should I just stick to the basics (slow acceleration, below 60, etc).
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Old 07-15-2011, 10:28 PM   #2
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Re: Automatics and Engine On Coasting...

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Originally Posted by chriswf View Post
Does anyone do coasting (engine on) in their automatic?

Is there a down side to it? (bad on transmission, engine, whatever).

Currently looking into a fiero. It will be automatic. But for daily driver purposes, I may want to drive to work for as little as possible.
Automatic okay for neutral coasting? Or should I just stick to the basics (slow acceleration, below 60, etc).
I don't really recommend it on the premise that the transmission might not shift safely/smoothly back into gear when you go from D to neutral. I just know that on the Volvo S60, it used to have the function of shifting into neutral every time the driver came to a stop, in order to save fuel. Unfortunately the transmissions started to fail very early like around 40K miles so Volvo initiated a software update to disable this functionality in order to preserve the transmission. It could have to do with their customers (while in neutral since they're at a stop) stomping on the accelerator and forcing the car to quickly shift into gear, putting too much load on the transmission and them not knowing or caring about it.

2007+ V6 Camrys have this feature as well and they too seem to be suffering from transmission failures (one I've experienced) though I haven't read anything that attributes the failures to this so it could be just a coincidence.
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Old 07-16-2011, 04:49 AM   #3
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Re: Automatics and Engine On Coasting...

Domestic transmissions handle it just fine. I did a little, experimenting but not hypermiling, in a 1987 Cadillac Deville (transverse engine with transaxle, 4.1 V8) and a 1997 Pontiac Grand Am (transverse engine with transaxle, 3.1 V6). I do it all the time in my 2002 GMC Sierra (classic RWD-style layout, 4L60E transmission), currently at 200,000 miles and I started about 30,000 miles ago.

If you're concerned, rev-match while re-engaging D and don't use neutral at every stop, just use it to coast while driving (because you can't rev-match from a stop).

Pay attention. I once shifted my GMC into R because I forgot I was already in N. Engine stalled, I put it back in N and restarted while continuing to coast, no damage...but I don't recommend it.

Of course if your equipment is marginal then I don't recommend trying anything out of the ordinary. Jay2TheRescue was downshifting hard for DFCO and blew his torque converter; I suspect that the non-rev-matched downshifts (can't rev-match a downshift in an automatic!) pushed his marginal torque converter over the edge.

Rev-matching is predicting the RPM you'll get once you're in gear and using the accelerator pedal to get your engine up to that RPM before shifting. In actuality there's likely a delay in the shift so you can probably do it while you operate the shifter.
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Old 07-16-2011, 08:43 PM   #4
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Re: Automatics and Engine On Coasting...

I had a 1994 Dodge Intrepid that i tried that on. I quit doing it. About the only time I coasted was when i was coming upto a sure stop which i was going to be there for awhile. It was just too hard on the trans.
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Old 07-16-2011, 09:34 PM   #5
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Re: Automatics and Engine On Coasting...

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I don't really recommend it on the premise that the transmission might not shift safely/smoothly back into gear when you go from D to neutral. I just know that on the Volvo S60, it used to have the function of shifting into neutral every time the driver came to a stop, in order to save fuel. Unfortunately the transmissions started to fail very early like around 40K miles so Volvo initiated a software update to disable this functionality in order to preserve the transmission. It could have to do with their customers (while in neutral since they're at a stop) stomping on the accelerator and forcing the car to quickly shift into gear, putting too much load on the transmission and them not knowing or caring about it.

2007+ V6 Camrys have this feature as well and they too seem to be suffering from transmission failures (one I've experienced) though I haven't read anything that attributes the failures to this so it could be just a coincidence.
Hmm... I wonder if my wife's Scion tC has this feature. When you hit the gas hard from a dead stop, it'll jerk as it re-engages back into gear (automatic).
Even if you're coasting in drive on the highway, it'll pull out of gear, and if you push the pedal too fast, you can feel it jerk.
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Old 07-18-2011, 07:54 AM   #6
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Re: Automatics and Engine On Coasting...

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Pay attention. I once shifted my GMC into R because I forgot I was already in N. Engine stalled, I put it back in N and restarted while continuing to coast, no damage...but I don't recommend it.
Find out where the gates are on the shifter. I'm sure many don't know this, but it isn't always necessary to to pull the shifter towards you or depress a button to shift gears in an automatic. Depends on the model, and the info might be in the manual.

I can freely shift between neutral and drive in the HHR, but have to press the shift button to enter reverse or lower gear. It was the same in the Ranger. So I didn't have to worry about going into reverse while in motion. On the other hand, the wife's Sable doesn't freely shift like that. So I rarely neutral coast in it.
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Old 07-18-2011, 08:52 AM   #7
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Re: Automatics and Engine On Coasting...

I agree about the gates, and usually I remember to mention that in threads like this. I made a mistake that time (easier in my truck than others due to angle/position of shifter, I think).
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Old 07-22-2011, 02:01 PM   #8
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Re: Automatics and Engine On Coasting...

Well, I took my mother-in-laws 1998 4000 pound plus Dodge Grand Caravan to deliver a package and do another errands today. She does not drive it much so I wanted to get it nice and warm. Her mpg was 11.3! I reset it before I started, 4 miles of stop signs/lights before getting to the freeway, then 28 freeway miles, 1 mile to objective. 28.5 mpg. Its a automatic, no eoc, just drafting, go 55, shoe off. On the way back tried putting it in neutral
while drafting, rev match to reengage. It worked better than i thought, reading range of 35 to 99 mpg before putting it back in gear. 29.1 mpg home. Did not seam to cause any problems with the trans doing rev match. I could now see how the mpg leader here can do it in his automatic.
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Old 09-03-2011, 09:25 AM   #9
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Re: Automatics and Engine On Coasting...

I do this on both my 2004 Tacoma prerunner and my parents 2011 ES350 without any issues. My Ultragauge reads 239 mpg for a few seconds coming down the pass in "N". All I have to do is wait like 3 seconds after I put it back into "D" before pushing the gas pedal, otherwise it will jerk. Th ES 350 shifts back as smooth as butter however.
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Old 09-03-2011, 03:52 PM   #10
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Re: Automatics and Engine On Coasting...

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I do this on both my 2004 Tacoma prerunner and my parents 2011 ES350 without any issues. My Ultragauge reads 239 mpg for a few seconds coming down the pass in "N". All I have to do is wait like 3 seconds after I put it back into "D" before pushing the gas pedal, otherwise it will jerk. Th ES 350 shifts back as smooth as butter however.
Well I decided to stick to manuals for coasting. Even if I decided to do an engine swap in my Fiero (and it needed a stronger automatic tranny).

I do manual coasting a lot now. Especially when I get low on gas (little below 1/4 tank), and I don't want to hit the pump up. I'll start engine off coasting with windows up. Red light predicting. Lighter acceleration. Etc.
Oh how lazy, it's beautiful.
But it can easily add 2-3 days onto my fillup date.

But engine off coasting works great for manuals. But regular neutral coasting for automatics doesn't seem right.
-- I've read elsewhere that people do this and it can cause problems like "passing gear not engaging" or something. Evidently this guy did it for a while in his old avenger. Then his car quit shifting into low gears when he went to pass someone on 1 lane highways. It would just shift OUT and rev really high.
His transmission mechanic said it was due to an "unexplained transmission damage".

I don't know. But I guess it's deal with it for automatics, or drive (coast) manuals for me.
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