Neutral to drive coast, is it bad for newer auto trans
 

I would like to start dropping my automatic transmission into neutral to coast to stop signs. Problem is I'm not sure if its safe if I have to go back to drive while still in motion. I have an 07 Malibu, and its not worth it to me if I'm doing any sort of extra wear and tear on the trans. Your expertise is appreciated. :confused:

...which transmission do you have in your '07 Malibu? The current 6T40 (RPO: MH8) didn't come out until 2008 in the Malibu.

...quickest answer is ask your dealership if the transmission in your Malibu has "input pump" only...which means the lubricating trans fluid stops moving when the input (from torque converter) shaft stops...meaning no-fluid flow = no lubrication = things can fail.

...as a "general" statement only--if the car has to be dolly-towed, because the FWD wheels shouldn't be rotating while towed, the transmission should not be coasted-in-neutral for either long distances or at high speeds.

I thought this was only for engine off coasting? Or is it a problem with the engine on as well...

Yes, just engine off. I've been engine-ON coasting with my automatic for a while, and it has the pump on the input shaft.

In any case, it takes practice, but if you can do it smoothly it shouldn't be a problem. I've been doing it everyday for a year or so with my notoriously unreliable O1M VW automatic and it has not developed any issues (yet).

...:o Yes, you are correct, I didn't describe it (...when the input (from torque converter) shaft stops...) well enough, sorry. Engine OFF is problematic.

I hae 255,000 miles on my Infiniti Q45 and have coasted (engine on) for 210,000.
Still have the same tranny.


I will say that a drove a ford tarus 2009 and it didnt like neutral coasting.

...most of the "older" automatic transmissions had both front & rear hydraulic "pumps" so the car could be push/bump-started. Many of the "newer" AT's now only have a "front" pump, so when the input isn't turning, there's no fluid pressure or flow.

...which type transmission do you think the Infiniti Q45 has?

My experience, I did this with my wife's van. It cost me $2000, to put a new transmission in. The amount of money you can save, just isn't worth the risk, IMO.

And with both of my GM's N coasting over D coasting has no advantage, or at least so small not worth the effort.

What you describe should cause no harm, but here's what you need to know. The potential problem comes not with putting the transmission into neutral and coasting, but rather when you re-engage it into drive. If you coast to a stop (or an almost stop, meaning below 10 MPH) there will be no harm incurred.

Most automatics are designed with the intent of being shifted from neutral or park into drive, as starting from a standstill. The potential problem arises when you are moving at speeds much greater than that 10 MPH threshold of first gear. I once asked the same question of a transmission technician and he told me the torque converter cannot determine how to handle the sudden transition from neutral into a much higher gear. In other words you not only risk damaging the transmission but the torque converter as well. However if you coast to a stop (or an almost stop) before re-engaging back into drive, there should be no problem regardless of the transmission design.

I've been doing this for a long while now on my four cars (all are automatics) and have found no problem from doing it. However, bear in mind that if the stop sign that is your target point is 1/4 mile off and someone pulls out at a slower speed in front of you while you are going 40 MPH, you probably will need to coast back down to 10 MPH before re-engaging into drive. Thus I never coast to traffic lights - because if the red light turns green while you are approaching it at 30 in neutral, your options are few because you can neither go back into drive nor accelerate.

In my experience neutral coasting an automatic does help improve FE somewhat - but the situations where you can implement it are limited, as traffic often makes it impossible to do.

And (of course) your going to tell us the make and model of the Van???????

Starting in mid-2002, JATCO introduced the RE5R05A:
a rear-wheel drive, 5-speed automatic transmission used in the Infiniti Q45.
Since then, this unit has appeared in Infiniti and Nissan drivetrains.
Infiniti uses it in CX25, FX35, FX45, G35, M35/35x, Q45, and QX56 vehicles.
Nissan uses it in the 350Z, Frontier, Pathfinder, Armada, Titan,and Xterra.

I can shift in and out of neutral at any time and any speed on the Q45.

This is my understanding based on nothing but driving impressions of various vehicles. When I try to drop back into drive on my Dodge Ram, the engine races and the truck rapidly decelerates as it thinks about shifting into a higher gear. Other cars such as the Toyota Camry don't appear to exhibit this behavior.

While I don't have any hard evidence one way or the other, I would say if it feels harsh, it probably is. If not, you are probably fine.

Engine on coasting in an AT equipped car or truck depends on the vehicles ability to reengage the transmission without any trauma. My 08 Altima would reengage easily with almost no perceptible deceleration. It did this by engaging in the highest ratio (CVT) with the torque converter lockup disengaged. Even at 70 MPH the initial engagement would get the RPM to increase from idle (700) to about 13-1500, then after about another second or two the RPM would increase to the same level as it was when you were driving at the same speed. Worked fine up to 80 MPH. I never tried it above that speed.

regards
Mech

Hi UFO,
I'm newly registered here to ecomodder (long time lurker) and happened to run across your recent post on the coasting in neutral with the VW 01M transmission and wanted to pick your brain on some tips. I have a 2002 VW jetta 2.0 with the 4 speed trans as well. I've had a heck of time just getting the mpg to increase from an average 20-21 to 26-28, which took replacing nearly all known mpg influencing parts and getting the scangauge, but I feel I'm still limited by this darn transmission.

Hence, it was good to see someone with the exact same transmission since I feel that is the major limiting factor on these cars. What sort of tips have you done to overcome this? i.e. what were your optimal speeds/gears. I've found 50-55 is the sweet spot. I've starting coasting in neutral with engine on as long as I'm coming to a stop.

Any help would be greatly appreciated!

I increased my mileage from 37 to 45 partly due to my engine-on coasting, partly due to my slowing down and timing my stops. Given the limitations of the VW O1M, I don't think I am going to be able to make many further improvements with driving technique. It looks like you may have hit the limit of yours as well.

One major goal of mine when driving in traffic is to get up to the overdrive shift points as soon as practical, and stay there. My first overdrive shift point is 30mph indicated, and I can drop 2mph and still stay in OD. The final overdrive shift point is 42mph, and I can drop down 3mph while still staying locked up.

If I anticipate a light is going to change, but I cannot hit it while staying in lockup, I disengage the tranny and coast to the light, hopefully maintaining my momentum as I get to the light. As soon as it changes, I reengage the tranny (NO accelerator!) and wait 2 seconds for the hydraulics to fill, then re-apply the accelerator to get back to my shift point.

If the light is not going to change, I leave the tranny in gear and engine brake to the light before shifting into neutral to wait for the light change.

If the O1M decides to break, I will probably do a 5 speed manual conversion. For some reason, the VW automatics get worse mileage than most other manufacturers' automatics.

Thanks for the help. You make good points for getting to the highest overdrive as quickly as possible. Since getting the scangauge, I've noticed there is a tremendous jump in FE when making it into the 3rd and 4th gear.

Do you tend to speed up to these faster than the preferred 1.5-2gph since the gain in mpg is so substantial?

I've done this in my AT Saab. It will take your transmission from potato salad to jello. On which ever speed you re-engage your transmission there will be a dull spot at that speed that may or may not go away eventually. That'll make your transmission less responsive and require more finessing and more accelerator to get up to speed. You won't shift as readily or as fast and it'll shift at a slightly higher speed and rev. (And i'm talking doing this 10 or less times in total)

Maybe some rare cars are designed to do this without wear, but i think the categorical recommendation should be do not do it!

Do:

Sell your car.
Buy a more fuel efficient model with a manual.
Stop wasting your time trying to coax more from a cast iron tub with wheels as is my case.
Do it sooner and you'll save more gas.

Hasn't happened yet; I've been coasting every day for over a year now. As far as "wasting your time trying to coax more from a cast iron tub with wheels", that runs contrary to the spirit of this site, where we do the best we can with what we have. It might be cheaper for you to switch cars, but I assure that is not the case for most drivers, especially for me as fuel is extremely cheap as it is made from free recycled vegetable oil. If I were to get 10mpg better economy with a manual transmission, at $1 per gallon of fuel, and a straight vehicle trade, it would still take more than 3 years to pay the extra registration fees and taxes associated with buying a different car.

Not to mention the person who ends up with my old car would not get the mileage I did. ;)

I will typically accelerate briskly but not so fast that my rpms exceed 2500 (I have a diesel); you might consider staying under 3000, but I haven't much experience with VW gas engine efficiency. But in traffic I accelerate slower than the car in front of me because that 5-7 second gap is the space I need to coast or engine break during speed variations.

Interesting descriptions for AT feedback. On my 09 Corolla it needs to be engaged in D so that it can engage DFCO (deceleration fuel cut-off). From highway/normal city running speeds all the way down until ~20kms/hr (15mph) once you lift the throttle...it reads zero, then at this lower speed point mentioned I can actually feel it start feeding fuel to the engine again and see that reflected on the gauges. If I put it into N it continues to consume fuel at near 1000rpm the entire time. The dash fuel consumption readout and scan-gauge II confirm this.

This DFCO is very handy in the winter as well as it acts like gearing down in a manual transmission setup and feels a lot like engine braking.

Considering this built-in feature I have no desire to turn off the engine to coast down either and my understanding of AT is that it needs to have ATF pumped through it to provide cooling and correct operation. Lastly, I would want to have full driving functionality to be safe, I feel that engine off removes this functionality.

I meant no offense. When i said wasting time with a cast iron tub on wheels, I was talking about myself.

@Leanburn -- I use DFCO (what I referred to as "engine braking") when I have to slow down, but it saves more fuel to coast with the engine on when you won't have as much momentum to regain.

Make no mistake, DFCO sacrifices momentum, using it to keep the engine turning without fuel.