manual coast with automatic tranny

seekinshadows · Oct 12, 2010

Hi all,
I know this has been addressed before but I can't seem to find a straightforward answer while sifting through all the posts.

What I want to know is this: Will it hurt my Riot engine or transmission if I coast in neutral down hills (not really steep ones) and coming up to red lights/stop signs if I have an automatic transmission?

I heard yes and I've heard no. I've been doing it for about 2 weeks now and I've increased by mpg anywhere from 3-4 mpg, even while doing a lot of mountain road driving.

DReynolds86 · Oct 12, 2010

Snapping it back into drive while the vehicle is in motion will lead to long-term transmission problems, yes. Or at least that's my understanding of it.

the_jeep_now · Oct 12, 2010

I'd say yes it'll hurt your tranny. Automatic transmission or CVT in your case should be shifted only at a full stop. My friend used to do this on his old Honda and after a while it started skipping gears. My advise don't experiment with it espicially how pricey it is to replace one.

tiptronic · Oct 12, 2010

If you need to play around with the stick while you are driving , buy a manual box. I you forget & you accidentally select P or R whilst on the move it'll be " Goodnight Vienna " to your CVT , also it isn't good or recommended practice!

sskelmar · Oct 12, 2010

tiptronic said:
If you need to play around with the stick while you are driving , buy a manual box. I you forget & you accidentally select P or R whilst on the move it'll be " Goodnight Vienna " to your CVT , also it isn't good or recommended practice!

Computer control wont let you shift into park whilst on the move, but I agree it is not good for the tranny to coast in neutral.

benefactr · Oct 13, 2010

Seems like this method has been debunked to increase your gas mileage. Just let your foot off of the gas when coming to a stop and coast in.

Medic311 · Oct 13, 2010

putting your car from D into N while moving is fine, however snapping it back from N to D while moving does serious damage to your transmission (at least traditional planar gear transmissions) and enough of that behavior will lead to complete transmission failure down the road.

to be honest, i'm not sure about shifting like that with the CVT, however i can't see how it would actually help anything. the transmission is designed to be the most efficient when in proper operation. once you start fiddling around with engagement / disengagement now you have stepped outside of the designed scope of operation and can do more harm than good.

less shifting = less wear and tear = longer life span

this is why while in bumper to bumper traffic for a significant amount of time it is actually beneficial to drop the gearing down to low or 1 etc, to guarantee that the transmission won't jump gears due to acceleration demands from some brief movement ahead of you. less wear and tear on the transmission

Afmcronnie · Oct 13, 2010

At highway speeds I would think that you would save MORE gas by leaving it in gear and letting the RPM stay above 1500 while coasting. The computer cuts off fuel flow to the injectors in this situation. No fuel flow means NO fuel flow. This is even more efficient than idleing. Might be hard to do with an FDII, no Autostick......

todde702 · Oct 13, 2010

From a mechanical perspective, I don't see it causing any damage, or rather any additional damage then normal shifting would do. On a traditional automatic, there aren't any "gear changes" inside, just different clutch pack or band engages to turn the planetary gear different ways. These are hydraulically controlled and most use some sort of spring loaded piston to buffer the engage. So long as engine speed is low that is. If you are revving the engine way high and "neutral slamming" then yes, damage can occur. I would think the CVT would be even more resilient to this since it's a belt designed to slip some. Also, since the vehicle speed determines the "gear ratio", the cones should be where they need to be upon engaging drive.

As Afmcronnie stated though, the ECM will cut fuel on coast so long as the engine speed is above 1500 rpm, so you may be best to shift into 6th or 5th on the CVT (if you have a FDI) for the down hill coast. The higher gear ratio should give you a longer coast time and keep rpms up with little brake pedal apply.

Experiment some and let us know what you find.

seekinshadows · Oct 13, 2010

It actually does save a bit of gas, but I guess it could be of course because I live in Colorado and there are a lot of hills in Denver. This last tank of gas, I got 5 mpg more than normal, and I have been tracking my mpg almost every fill up since I bought it a few months ago. So it's not a myth.

I have a FDII so the 5th/6th gear isn't an option, unfortunately.

dixiedawg · Oct 13, 2010

I understand as I have some good 4-8 mile downhills myself. I have been afraid to try it in the Patriot though.

My sister in law just came in for a family funeral, and invited us to come visit her in Denver. Not sure when I'll go, as I'm planning on Alaska for next year, but soon I hope.

seekinshadows · Oct 18, 2010

Ok, I've tested both methods, coasting in neutral and trying to keep the RPMs below 2500 and the RPM method works better, although I get more honks, screams and middle fingers, LOL.

Dawg, if you head this way during the summer, you'll have to check out Indian Peaks Wilderness area. Beautiful drive and not too far from Denver!

manual coast with automatic tranny

seekinshadows

DReynolds86

the_jeep_now

tiptronic

sskelmar

benefactr

Medic311

Afmcronnie

todde702

seekinshadows

dixiedawg

seekinshadows

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