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:
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.
I remember being a passenger in a military CUCV and steciled on the dash was "DO NOT IDLE IN PARK"
Thanks for the info -- 2 more reasons to buy a Ford.
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.