USMC46
Richmond, Tx.
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Joined: 08/31/2006
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I have what may appear to be a simple driving habit question.
When traveling through cities with multiple stop lights, is it best to leave the transmission in drive gear at long stops, or put transmission in neutral at each stop if light is expected to be relatively long light ? Transmission is Allison six speed in 41' DP.
Thanks
Jim & Carmel
2004 Dutch Star 41'
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Lug_Nut
Newmarket , Ontario, Canada
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Jim, You should not need to shift out of gear for any short travelling stops. The only time I would think of shifting into neutral, is if a traffic hold-up is causing 5 minute delays, etc. In these cases I also always apply the parking brakes also
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ddreisbach
Kemah, TX
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Shifting into neutral at stoplights will improve your gas mileage by reducing load on the engine during the time you're sitting there.
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helperzack
Port St. Lucie, FL
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I am not a mechanic, however, one once told me to never put in neutral while sitting. For what it is worth, he said that "when in neutral the fluids are not circulated."
So, I just don't do it. If sitting for a while just put into park.
Does anyone know any negatives of just putting the parking brake on when in this situation? One would think none?
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KOG
Winterville GA
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Shifting an automatic into neutral has no perceptible effect on fuel consumption unless you turn the engine off as well. And turning the engine of has little effect on fuel consumption of a diesel unless you're parked or an extended period. Turning engine off will have a slight effect on fuel consumption of a gas engine.
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j-d
Sunny Florida USA
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I put our old gasser in N if stopped for more than a minute or so. Especially if it's hot and I have dash air running. Engine idles at a higher speed hence the engine fan and better flow over the a/c condenser. I don't shut it off - Old gasser just might not start! I think Park is nothing but Neutral plus a mechanical lock on the output shaft so the vehicle can't roll. If fluid wasn't circulating it wouldn't have hydraulic pressure to go back in gear.
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goodcruisin
Greenwood, IN
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helperzack wrote:I am not a mechanic, however, one once told me to never put in neutral while sitting. For what it is worth, he said that "when in neutral the fluids are not circulated."
So, I just don't do it. If sitting for a while just put into park.
Does anyone know any negatives of just putting the parking brake on when in this situation? One would think none?
The one who told you that is wrong. The input shaft of the transmission drives the sun gears which in turn drives the oil pump. Fluid is circulated anytime the engine is running regarless of the gear that is selected.
Shifting into neutral takes the pressure off of the transmission allowing the fluid to circulate through the trans and torque converter more freely thereby reducing heat.
It doesn't harm to put the trans in neutral. If I'm going to be sitting for a few minutes I shift into N and apply the parking brake.
John (USN Ret) and Debbie
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mowermech
Billings, MT
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goodcruisin wrote:helperzack wrote:I am not a mechanic, however, one once told me to never put in neutral while sitting. For what it is worth, he said that "when in neutral the fluids are not circulated."
So, I just don't do it. If sitting for a while just put into park.
Does anyone know any negatives of just putting the parking brake on when in this situation? One would think none?
The one who told you that is wrong. The input shaft of the transmission drives the sun gears which in turn drives the oil pump. Fluid is circulated anytime the engine is running regarless of the gear that is selected.
Shifting into neutral takes the pressure off of the transmission allowing the fluid to circulate through the trans and torque converter more freely thereby reducing heat.
It doesn't harm to put the trans in neutral. If I'm going to be sitting for a few minutes I shift into N and apply the parking brake.
The pump is driven by tangs on a tube attached to the torque converter housing. The sun gears are in the planetary gear sets behind the pump, inside the transmission housing, and have nothing to do with pump operation. The transmission input shaft is not attached to the pump, either.
The hydraulic circuits inside a transmission can be very complex, and general statements are often wrong, due to the differences in construction. SOME automatic transmissions do not circulate oil to the cooler when in Neutral or Park. Since that oil is what lubricates some of the moving parts, extended idling in Neutral CAN be detrimental. It would probably take several hours at a time to hurt anything, though. A few minutes at a stop light won't damage anything, IMO
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geezer34nh
New Hampshire
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Just to ad a bit to the above. The shell of the torque converter is bolted to the flywheel. The front pump in the transmission is driven by the shell of the converter so there is fluid being pumped through the transmission all the time the engine is running.
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mowermech
Billings, MT
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geezer34nh wrote:Just to ad a bit to the above. The shell of the torque converter is bolted to the flywheel. The front pump in the transmission is driven by the shell of the converter so there is fluid being pumped through the transmission all the time the engine is running.
True, the hydraulic system is pressurized whenever the engine is running, but in SOME transmissions, not ALL the circuits have oil flow when the transmission is in Neutral or Park. The oil cooler/lubrication circuit is one of those, in SOME transmissions.
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