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Thread: Vehicle Idling "neutral" vs "park"

  1. #1
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    Default Vehicle Idling "neutral" vs "park"

    OK - If you are forced to idle a vehicle with an automatic transmission for a long period of time while parked, is it better to but the vehicle in "neutral" or "park"?

    I remember being a passenger in a military CUCV and steciled on the dash was "DO NOT IDLE IN PARK"

  2. #2
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    I don't think it really matters.
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  3. #3
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    Probably some weird transmission quirk with whatever the transmission was. Something that was spinning and didn't get oil if it wasn't in gear or something like that..

  4. #4
    Neutral is better, on a military Hummer it is due to the piss poor cooling system they have . . . being in park the torque converter input is spinning and the output is stationary due to the gears being "locked" in park. This generates a lot of heat in the fluid that the system is not really able to easily get rid of . . . if you are in neutral the converter is spinning freely and less heat is being produced by the tranny . . .

    So it's just a matter of whether your cooling system is capable of getting rid of the heat and how often you like to change out tranny fluid

  5. #5
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    Quote Originally Posted by Skratch View Post
    Neutral is better, on a military Hummer it is due to the piss poor cooling system they have . . . being in park the torque converter input is spinning and the output is stationary due to the gears being "locked" in park. This generates a lot of heat in the fluid that the system is not really able to easily get rid of . . . if you are in neutral the converter is spinning freely and less heat is being produced by the tranny . . .

    So it's just a matter of whether your cooling system is capable of getting rid of the heat and how often you like to change out tranny fluid
    Never heard that one before, but then again it does make sense.
    "Not all those who wander are lost."
    J.R.R. Tolkien

    "Money can't buy you happiness...
    but it does bring you a more pleasant form of misery."
    Spike Milligan

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  6. #6
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    depends on what I'm doing or driving.

    I tend to idle in park, IF i have to idle.

    When I have winched offroad, I idled in park.
    "For He so loved the world, that He sent His only son..."

    Brian
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  7. #7
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    Check the dipstick. If it says "Check fluid with the transmission in Park", don't idle in park.

    Dodge transmissions do not circulate fluid through the cooler when in Park. That is why the dipstick is marked to check fluid with the transmission in Park. If you don't do that the fluid reads high and you get an incorrect reading. Some will find this hard to believe and call BS. I have had to prove it to quite a few. It is easy to see with it connected to a fluid exchanger. The fluid clearly stops circulating through the cooler when the transmission is placed in Park.

    You can really see a huge difference in one that has not been left to idle in park. Idled in park really cooks the fluid. I preach to everyone in my fleet, either idle in neutral with the parking brake applied, or shut it off.

    Dodge transmissions are also the only ones left that require the bands be manually adjusted every 20k miles. Kind of a pain, but at least the filter gets changed regularly on that schedule.
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  8. #8
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    Quote Originally Posted by HenryJ View Post
    Check the dipstick. If it says "Check fluid with the transmission in Park", don't idle in park.

    Dodge transmissions do not circulate fluid through the cooler when in Park. That is why the dipstick is marked to check fluid with the transmission in Park. If you don't do that the fluid reads high and you get an incorrect reading. Some will find this hard to believe and call BS. I have had to prove it to quite a few. It is easy to see with it connected to a fluid exchanger. The fluid clearly stops circulating through the cooler when the transmission is placed in Park.

    You can really see a huge difference in one that has not been left to idle in park. Idled in park really cooks the fluid. I preach to everyone in my fleet, either idle in neutral with the parking brake applied, or shut it off.

    Dodge transmissions are also the only ones left that require the bands be manually adjusted every 20k miles. Kind of a pain, but at least the filter gets changed regularly on that schedule.
    Thanks for the info -- 2 more reasons to buy a Ford.

  9. #9
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    Quote Originally Posted by sargeek View Post

    I remember being a passenger in a military CUCV and steciled on the dash was "DO NOT IDLE IN PARK"
    When was this? Reason I ask is that the predecessor to the CUCV was the M-880 Truck (The M880 was a 1975 -76 Dodge 3/4 ton truck with a 318 gasoline engine, auto tranny and full time 4wd.) Those M880 series trucks had notoriously bad automatic transmissions that would indeed burn up if you let them idle in park and most commands had the "do not idle in park" directive spray painted on the dash.

    The M880 was taken out of service in the mid to late 1980s when the CUCV (M1008, M1009 and M1028) trucks were introduced (CUCV: 1985-87 Chevy 3/4 ton pickup and Blazer with a diesel engine, auto tranny and part time 4wd.)

    The last time I saw an M880 on active service was in 1990 when I was in Korea for Team Spirit. We had to unload some trucks from the railhead at Chunchon. The trucks belonged to a Reserve or NG unit and some of them were M880s with the "do not idle in park" command painted on the dash.

    Just a guess but I'm wondering if the vehicle you were in was actually an M880?
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  10. #10
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    I don't know exactly what vehicle it was. I was looking for deals at the the Denver DRMO at Rocky Mtn Arsonal in the mid 90's. Its just one of those weird items that stuck in my head. I was curious if it would be worth adopting the practice in my personal vehicle. And with the diverese experiences of this board I could get a decent response.

    So it seems like it would still be a prudent practice to idle vehicles in neutral with brake applied.

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