Is coasting bad on my Automatic transmission?
 

I drive an automatic 98 pontiac sunfire.
I just recently started hypermiling and just did a 1000 mile round trip from OH to VA and back to see my GF. i averaged a ridiculous 40mpg with the round trip im assuming because of all the down hill i had both ways...(plus i drove like a p*ssy about 90% of the time):turtle: the last 200 miles i actually averaged 55mpg..it was ridiculous.:eek:

anyways..getting to the point of this thread...
Like i said there were lots of crazy downhill grades, some lasting 9-12miles where i coasted in Neutral literally the whole way, and then shift back into Drive while moving relatively fast so i can slowly build speed to make it up the next hill.

My Question::confused:
Is it bad to shift from D to N and back to D while moving in an Auto Transmission car? i have been told yes and no...:(

as you can tell i am relativly new to the idea of hypermiling and know very little about cars, altho i wish to learn. dont exactly know where to start...:p
Thanks in advance :)

If you leave the engine on,it should be ok to coast in N.
D to N,I don't see anything that is stressed.
N to D well does it engage smooth when you go back to D?
If so,it should be ok as well. If for any reason there is a clunk,jerk whine whatever does not feel right when going back to D, in that case I wouldn't be doing it too much.

Because there are so many things in an A/T that can wear at different rates and effect shift timing or engagement of components ( servos,pistons,springs,clutches,seals etc.) that's why I would go by feel and your own judgement instead of a rule of somekind.
On the plus side if you do blow up the trans,it will be a good excuse to get something with a proper manual tranny :D

Basically it depends on how the transmission provides lubrication for it's internal components.
In many the primary pump is directly behind the torque converter and is providing lubrication whenever the engine is running. This means if you coast with the engine off your transmission has no pressurized lubrication which will be disastrous when you transmission fails from lack of lubrication.
Some say if the owners manual says your car can be flat towed (drive wheels on the ground) it will be OK to coast with the engine off. I am not sure it's a good idea and the cost of a bad decision can be extreme.
Engine on coasting should be no problem as long as your transmission can handle going into gear at the end of your coast.
My position is engine on OK, engine off not OK.

regards
Mech

I appreciate this topic because I have been wondering the same thing. I obviously coast longer and have less load on my engine in N. But any fuel savings are rapidly erased by a damaged transmission. I have no clunking back from N to D, in fact I always seem to be in the correct gear no matter what speed I shift back to drive in.

Engine on = fine.
Engine off = it depends on the car. Check the owner's manual for towing instructions (like old mech said).

For the record, most Hondas specify flat-towing is ok up to 50 miles and speed below 35 mph. I use engine-off coasting in town, but engine-on for the highway. (driving the Odyssey auto. My manual civic gets multiple EOC's every mile, at any speed)

The trans should be fine and ignore the +1 for yes as i clicked that then switched to No but did not realize that there could be multiple selections.

Thanks so much guys,you were extremely helpful!
i appreciate it a lot.
everyone still feel free to chime in with your opinion...or if anyone here has a 98 sunfire just like me, maybe you can give me some tips.

On both of my GM's fuel use stays the same coasting in neutral or drive, so I leave them in drive, the Stratus need neutral to coast well, it downshifts while coasting in drive.

Right. GM transmissions go into a "nearly neutral" mode automatically. That's a good thing. Many others, like your Stratus and most Hondas, hold the gear and even downshift to provide engine braking instead. You have to fight that to get the best mileage.

I drive a 2000 Civic with an auto trans. I've been trying ignition off coasting / P&G a bit, and it doesn't seem to be doing anything nasty to the transmission. Here's what I do:
* Build up to 60 MPH (in a 55 zone)
* Put the transmission in neutral
* Turn the key from ON to ACC
* Turn the key back to ON (but not through to START)
* Coast (profit...)
* At 50 or 55 (depending on traffic conditions), turn key to START, engine comes on in neutral
* Shift to drive, extremely smooth, RPMs go from idle at around 800 to around 1800.

My car can be flat-towed for 500 miles when put in neutral from drive. Towing in neutral shifted from reverse is really bad for it. Also, steering doesn't lock unless you go past ACC (to OFF) on the ignition. Power steering goes away unless the engine is running, so there's that. And brakes lock up after 4 or so pumps. Those both come back immediately when the car is turned back on. I am a bit concerned about the starter, and I'm wondering if I can just pop it into Drive to start the engine. I don't really want to try that at highway speeds though...

I'd really like a definitive answer for Honda Civics or any other cars that can be flat-towed. I might just try it and take the risk for a few thousand miles, since I really don't think this is hurting my transmission. But, if I'm wrong, please correct me!