I've found an automatic that doesn't like neutral coasting

[theholycow]

It's pretty common for people to react with irrational fear when someone proposes using the 'N' position on an automatic. Most suggest that the transmission will break, which is just not the case; the way 'N' works is pretty much the same way the transmission always works as it shifts between gears anyway. One person recently suggested that idle speed at the input shaft is just not enough pump speed to keep the transmission completely cool, and that has been the only argument that has convinced me that there could conceivably be something to worry about.

Consider my wife's 2000 Isuzu Rodeo. It's an all around awful vehicle; I blame this partly on bad design and manufacturing by Isuzu, and partly on it beinig a rebuilt salvage vehicle (we got it for free, so really...can't complain too much!). It's got a V6 and a four speed automatic. She was practicing P&G and getting 22mpg (up from 18) when her "A/T Temp" light came on. She does not do it any more.

So there you have it. Finally there has been an actual data point showing that one vehicle's automatic doesn't like neutral coasting at speed. It didn't break, it didn't blow up, it didn't eat babies...it just warned the driver with a light to say "don't do that".

[Jay2TheRescue]

That's suprising... I always thought trucks lent themselves quite well to P&G... They are usually built with a good dose of overkill on the cooling systems, and in the case of my Beast, that has the Z71 off road package, and the towing package with the oversized radiator, external oil cooler and external transmission cooler.

-Jay

[Lug_Nut]

Possibly the added heat of the pulse phase, coupled with the reduced fluid flow through the cooler during the glide phase is the problem.
Have you checked the AT cooler fins for air flow restrictions that might make a otherwise acceptable heat fluctuation produce a high temp warning?


Are these last two posts Sterling examples, or what? .....

[bobc455]

Holycow, when you shift back into neutral do you rev up the engine first? Or do you just shove it in gear and let the tranny increase the engine speed?

-Bob C.

[theholycow]

I forgot to mention that she said the engine has stalled a couple times while shifting into D.

I haven't checked the cooler.

I haven't driven it much. When I did, rev-matching was difficult, as the engine balks and hesitates at the idea of increasing its speed. I did not experience any roughness shifting into D, though, whether or not I attempted to rev-match.

Another odd thing about that transmission is that shifting into N sometimes makes the vehicle buck.

[tggroo7]

Originally Posted by theholycow

It didn't break, it didn't blow up, it didn't eat babies...it just warned the driver with a light to say "don't do that".

Idk, I've heard rumors of some lost babies when coasting in neutral in those Isuzus...gotta be careful with those.

[ihatemybike]

Maybe try a larger add on trans cooler? I added on to my van and it's helped to keep the temps low.

[theholycow]

Yeah, if she drove a lot and it would pay for itself, I'd install a trans cooler. As is, it's just not worth it. I doubt she drives 100 miles per week. Eventually, when we spawn (how am I ever going to explain EOC to my child?) I'm going to insist that we trade it in for something safer.

[Jay2TheRescue]

Originally Posted by theholycow

Yeah, if she drove a lot and it would pay for itself, I'd install a trans cooler. As is, it's just not worth it. I doubt she drives 100 miles per week. Eventually, when we spawn (how am I ever going to explain EOC to my child?) I'm going to insist that we trade it in for something safer.

Won't your child think its nornal, and ask their friend's parents why they don't shut off the engine while going downhill?

[ihatemybike]

I picked mine at a bone yard for $10.

[theholycow]

Originally Posted by Jay2TheRescue

Won't your child think its nornal, and ask their friend's parents why they don't shut off the engine while going downhill?

That's exactly what I'm worried about. Kid grows up thinking that's normal, next thing you know he's talking about it to everybody else and then I have to explain it, or trying it when he's 15 and already illictly driving without a license / 17 and has a bunch of distracting friends in the car...

I try to keep my EOCing to myself. I discuss it freely here, and there's a couple open-minded friends I have, but I don't let it go further than that. There's a lot of hate and absent-minded alarmists out there...and if you set too many people off it ends up on the news and in laws and next thing you know cops are trying to figure out if somebody is EOCing.

[theholycow]

Originally Posted by ihatemybike

I picked mine at a bone yard for $10.

Good point, but the wife would probably not allow me to monkey around with her car..

[ihatemybike]

She's not driving the right vehicle then. My wife just drove her vehicles before, but now that she has a Jeep she's a member of a forum, planning off-roading vacations, bolting on under body armor. I have to supervise and break a bolt loose sometimes, but other than that she wants to do all the work.

[shatto]

I've given up coasting with an automatic, as the engine revs up anyhow.
I do shift out of gear when stopped as it does reduce the load and therefore saves pennies of gas.
Good theory, eh?

[theholycow]

Originally Posted by shatto

I do shift out of gear when stopped as it does reduce the load and therefore saves pennies of gas.
Good theory, eh?

I've measured the difference with my fuel rate meter. It's tiny, but measurable.

How much does your engine rev up when neutral-coasting?

[Jay2TheRescue]

Even though the engine revs my Scangauge data seems to tell me that I get double the instant MPG ratings when I glide in Neutral. I just put a deposit on a new place today. On the way to work from the new place there are several good hills to coast down. One of them is just perfect. I figure I can probably glide for at least 1/2 mile or more. I expect my mileage to start climbing in the next couple of weeks after I move.

-Jay

[suspendedhatch]

Originally Posted by theholycow

it didn't eat babies...

Well there goes my theory.

[striegel]

We bought my wife a 2003 VW Jetta this past Summer and it displays some unfriendly behavior with coasting in N. There's some kind of brake-actuated gear lock that messes with the lever so that if you try to shift from N back to D, it doesn't actually make the shift even though the lever shows it should have.

I've found myself revving in N instead of moving away from a light. It requires a full re-application of brake and another shift from D-to-N-to-D to make it work right.

I wouldn't even bother except that this car's AT has LOTS of drag when coasting in D. Still, the fuel mileage is significantly better around town than the Odyssey -- that's why we bought it (when gas was around $4 a gallon).

[theholycow]

Interesting. Having a brake interlock for the N->D shift is nonstandard. How long do you have to apply the brake for it to happen? Do you just have to be on it enough to trigger the brake light, or do you have to really step on it well?

[dkjones96]

Have you checked the oil level in the transmission? Brake interlocks prevent the lever itself from moving, not the transmission from going into a gear. If it's revving in neutral like that there is probably something else going on...

[striegel]

The interlock seems to act right at the shift handle. You can hear it click in there whenever the brake lights are activated.

I would have thought it was only needed to prevent shifting from Park without having the brake applied, but it seems to also affect the N-D shift.

[theholycow]

So, you shift N->D, and only after you apply the brake you hear it click near the shifter and are able to accelerate?

There's a lot I like about VW, but I hate how overengineered some functions are.

[striegel]

Well, I haven't examined it scientifically, but I believe it goes like this:

Coasting in neutral to a stop, foot stays on the brake. When the light is set to change, I move the shift handle back to D and take the foot off the brake, moving to the accelerator pedal. Giving it the gas, I find that the transmission is actually still in neutral.

I think that if I shift back into D before applying the brake to come to a complete stop, it will accelerate normally. It's just when I leave it in N all the way up to and through the stop that it surprises me.

[striegel]

The Blue Box, by the way, is my point of reference. It behaves perfectly for coasting in N.