Hypermiling in a 2011 Elantra? Could some of the techniques hurt the transmission?
 

I am fan of hypermiling to save fuel. One of the steps is on downhill stretches or coasting up to a light that I know will be red, I’ll shift the vehicle from drive to neutral (and back to drive when I’m done with the downhill coasting). If I’m coasting up to a light that I know will be red for long, I will turn off the engine. I do this with my Honda Civic and Chevy Silverado. However, with my 2011 Elantra, there is a notice in the manual (5-17) to “Always come to a complete stop before shifting into D”. I’m aware that Hyundai has a new transmission in this vehicle.

So the question is: Can I still shift the Elantra into neutral from drive while the vehicle is moving and shift it back into drive from neutral while the vehicle is moving without damaging the transmission.

Thanks!

Maybe we need an item in the main FAQ "Read owner's manual thoroughly before purchasing a new vehicle".

I'm sorry I don't know the answer to your question about putting it in D when you're done coasting and still rolling. In my '89 Volvo (automatic) I found the trick was to put it back into Drive with my foot OFF the gas, that gave a smooth engagement. Attempting to rev-match gave a "hard" engagement.

However - regarding killing the engine to coast - it's important that you find the section where it describes if your car can be towed with the engine off and the drive wheels on the ground (rolling). Usually there's a limitation on both speed and distance. This tells you what you can do coasting an auto trans with the engine off. What happens is that the wheels "drive" the output end of the transmission. Depending on its design this can have the transmission internals rotating without the needed lubrication and fluid pressure. That's why they give you a speed/distance limit.

Maybe we do, but I hope you aren't thinking that I did not read the manual. If you noticed, I was quoting from a page. That might show that I did SOME reading, but the fact is, I've read the manual several times, plus going thru the index to try to find possible answers.

Yes you will be fine doing that as long as you aren't "revving" the engine while switching. Just let it idle for a second or two before you switch between idle and drive.

The transmission fluid pump is driven from the input shaft, and will obviously not be pumping if the engine is not running. That leaves 'splashing' or static immersion in fluid as the only source of lubrication. Will that be enough? Unless you're a transmission designer or accomplished mechanic, you have no way of knowing. I'd argue that unless the car has an unlimited speed/range towing rating, coasting with the engine off will be potentially damaging. Asking on a forum like this is not going to provide a correct answer; just because someone else has been coasting without immediately blowing up their transmission does not mean that their car, or yours, won't suffer some level of damage.

http://auto.howstuffworks.com/dual-c...ansmission.htm

Regor, I doubt anyone here could definitively answer your question, and you have a warranty to consider on a very expensive transmission repair and the possibility the cpu in your car could actually provide the manufacturer with information that would confirm neutral coasting.

My 2008 Altima is the ultimate coasting in neutral and shifting back into gear transmission (CVT-NEVER enigne off). Of course it shares little in common with your dual clutch 6 speed.

If you are willing to experiment with your new car, I would suggest trying shifting to neutral then back into drive at lower speeds, then progressing to higher speeds if you feel comfortable. With throttle by wire and a computer controlled dual clutch 6 speed at, it would seem logical that the transmission would shift into the highest gear when drive is reengaged. This should be confirm able from the tachometer reading.

My Altima seems to shift back into the highest gear, an overall ratio of 2.48 to 1 (including differential) with the torque converter unlocked. This results in a virtually perfect re engagement of the transmission, even at speeds as high as 70 MPH.

I would suspect your car would act in a similar fashion, but that is absolutely pure speculation on my part.

Today I enjoyed a 50 mile stretch of occasional opportunities to coast downhill in neutral, sometimes for .5 mile, then reengaging the transmission to maintain speed or accelerate very slowly. Over 40 MPG in a vehicle that is rated at 31 highway and smooth as silk transitions.

regards
Mech

If the clutches are "wet" I would not coast with the engine off. I think Ford has produced a dual clutch 6 speed that uses dry clutches, and actually has a neutral coast capability in the new model Focus.

In either case I would be very hesitant to coast with the engine off, unless you could confirm that no damage would occur, especially if it would void your warranty on one potentially very, very expensive transmission repair.

regards
Mech

Very well said. About 35 years ago I burned out the clutches in my A/T by coasting in neutral and shifting it back into drive at highway speeds. It was an expensive lesson I never forgot.

Being now older (and wiser?) I went to a transmission shop recently and asked them about neutral coasting and re-engagement into drive. They advised against it. The only method that is foolproof for coasting in neutral is to roll to a stop (or at least a virtual stop) meaning less than 10 MPH. When you shift back into drive it will go into first gear with no harm done.

From what I have read (not a whole lot) the dual clutch 6 speed is a manual transmission that has clutches controlled by a computer. If that is the case then neutral would cause no problems with lubrication of the gears, shafts, and bearings.

This is completely different from a conventional automatic.

The question is how are the two clutches controlled. I would ASSUME (sometimes a big mistake) the clutches are disengaged by hydraulic pressure. The reason for this is they are disengaged for a small amount of total operational time so that would be more efficient.

Wet clutches that are disengaged hydraulically may not work properly if the engine is not running to produce hydraulic pressure. The rest of the transmission being basically two 3 speed gearboxes combined should be fine without pressurized lubricant, but even that may not be correct, but it is probably correct.

I certainly would not want to be the first to experience a transmission failure, only to find that the manufacturer can avoid paying for any repair because they can prove you were using a method that is strictly prohibited in the owners manual.

If, like Fords DC 6 speed, the clutches are dry then I would feel more confident about neutral coasting. If the clutches are wet, I would probably not try engine off operation when the car was moving.

Typical band operated planetary gear set multi speed AT's require pressure to operate the individual gear sets, which without pressure would burn up fairly quickly, unless you leave the engine running.

On my car I have never and probably will never coast in neutral with the engine off, since the CVT requires hydraulic pressure to control everything, which I do not think is the case with a DC 6 speed, but you must also consider the computer controls may not function with the engine off.

Get a price on a new transmission if you decide to take any risk whatsoever. Probably over $5K.

regards
Mech

I've got 20,000+ miles on our 2012 Elantra limited (automatic) with lots of nuetral coasting even at highway speeds. No problems, changes or noises as of yet.