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

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Old 07-19-2008, 06:02 AM   #1
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Post I've found an automatic that doesn't like neutral coasting

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".
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Old 07-19-2008, 08:52 AM   #2
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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.

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Old 07-19-2008, 03:06 PM   #3
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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? .....
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Old 07-19-2008, 03:13 PM   #4
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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.
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Old 07-19-2008, 03:58 PM   #5
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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.
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Old 07-20-2008, 06:32 PM   #6
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Quote:
Originally Posted by theholycow View Post
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.
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Old 07-21-2008, 03:48 AM   #7
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Maybe try a larger add on trans cooler? I added on to my van and it's helped to keep the temps low.
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Old 07-21-2008, 06:51 AM   #8
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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.
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Old 07-21-2008, 07:10 AM   #9
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Quote:
Originally Posted by theholycow View Post
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?
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Old 07-21-2008, 07:12 AM   #10
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I picked mine at a bone yard for $10.
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