Vehicle Idling "neutral" vs "park"

sargeek

Adventurer
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"
 

dieselcruiserhead

16 Years on ExPo. Whoa!!
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..
 

Skratch

New member
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 :Mechanic:
 

KG6BWS

Explorer
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 :Mechanic:

Never heard that one before, but then again it does make sense.
 

BIGdaddy

Expedition Leader
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.
 

HenryJ

Expedition Leader
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.
 

SunTzuNephew

Explorer
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.
 

Martinjmpr

Wiffleball Batter
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?
 

sargeek

Adventurer
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.
 

1leg

Explorer
Thanks for the info -- 2 more reasons to buy a Ford.

WOW! haven't heard the first one yet..... :wings: (JK)

This all comes down to time I think, It is not good to let any engine sit idleing. Most owner manual i have read say that. So anything over a few(3) minutes it should be shut down and anything less shouldn't hurt anything.
If you are trying to charge the Battery or to get the heater going. It would be best to place it in "N" and run the RPMs up over 1500. Oh ya set the E-brake.

Thats My $.02.
 

Martinjmpr

Wiffleball Batter
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.

Yes, that would have been an M880, not a CUCV. AFAIK CUCVs weren't suplused out until the very late 90s or the early 2000's.
 

SunTzuNephew

Explorer
My Ford Superduty with the 6.4 Diesel has an option (Stationary Engine Idle Control) to speed up the idle speed while sitting around.....in park. Part of the logic requires the engine to be in park (neutral won't do it). It's originally designed to allow higher engine speeds for ambulances (to keep the alternator output up), it runs the engine at between 1200 and 2400 RPM, but is great for helping keep the cab warm too (of course, so do the heated seats). Hit the 3rd upfitter switch, and go to town!

And when the engine has been run particularly hard (towing, etc) you're supposed to let it cool down at an idle - it will shut itself off after 10 minutes of that, to keep the turbo from warping.
 

SunTzuNephew

Explorer
Yes, that would have been an M880, not a CUCV. AFAIK CUCVs weren't suplused out until the very late 90s or the early 2000's.


I got one (CUCV M1009 Blazer) from the Nellis DRMO in around 95 or so. It's amazing the ostensibly classified (code-word) stuff I found in little nooks and crannies (all of which was burned).

The one I got was in great shape....except for the transmission, which had a gas engine vac modulator installed, that didn't have enough adjustment range. It wouldn't shift from 2nd to 3rd until around 55 mph.....made for a miserable ride home.

A quick trip to the trans shop and it was fixed. This vehicle also had aftermarket AC installed, which was kind of nice. The CUCV's generally had horrible electrical systems, however - two 12v alternators, one run above ground to get 24v. If anything happened that brought that second alternator to ground, the batteries would both die. A lot of wildland fire departments that got CUCV vehicles surplus converted them to a decent electrical system, and sucked up the harder starting (the glow plugs and starter were the only 24 volt components, aside from the electrical bus for the radios in the passenger rear seat wall).
 

stioc

Expedition Leader
Personally, I hate idling in 'D' when the light just turned red. I always push it up to 'N'. Something about the engine pushing against the brakes bugs me. I hope the fluid circulates through the transmission cooler in 'N' in all cars?
 

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