Idle in P or N?
12-03-2006, 06:36 PM
#16
Registered User
Join Date: Oct 2005
Location: Bonner Springs, KS
Posts: 499
Likes: 0
Received 0 Likes
on
0 Posts
Why do you think this? Besides wasting fuel, you give a truck thief an easy target. The high idle feature was designed for quicker warm up from cold and extended idle periods when someone is in the vehicle and needs to stay cold or warm, depending on the season.
12-03-2006, 09:29 PM
#17
It circulates the same in park or neutral. From the service manual:
As the engine is running and the crankshaft is rotating, the flexplate and torque converter, which are also bolted to it, are all rotating in a clockwise direction as viewed from the front of the engine. The notched hub of the torque converter is connected to the oil pump’s internal gear, supplying the transmission with oil pressure.
With the gear selector in the NEUTRAL position (Fig. 4), the power flow of the transmission is essentially the same as in the park position. The only operational difference is that the parking sprag has been disengaged, unlocking the output shaft from the transmission case and allowing it to move freely.
As the engine is running and the crankshaft is rotating, the flexplate and torque converter, which are also bolted to it, are all rotating in a clockwise direction as viewed from the front of the engine. The notched hub of the torque converter is connected to the oil pump’s internal gear, supplying the transmission with oil pressure.
With the gear selector in the NEUTRAL position (Fig. 4), the power flow of the transmission is essentially the same as in the park position. The only operational difference is that the parking sprag has been disengaged, unlocking the output shaft from the transmission case and allowing it to move freely.
No, it does NOT circulate the same in park as neutral. The 48RE DOES NOT circulate fluid in park unless the VB is modified. Feed to the TC and the cooler are both 0 psi. Extended idling in park will destroy the pump gears and the TC hub.
The quote from the manual references power flow NOT fluid flow. Check the FSM, it clearly defines fluid flow in all the gears and what components are used.
Here is what happns when you idle too long in park:
12-03-2006, 11:28 PM
#19
Registered User
Thread Starter
Join Date: Aug 2002
Location: WA
Posts: 149
Likes: 0
Received 0 Likes
on
0 Posts
My question was about idle in P or N.
12-04-2006, 02:45 AM
#20
Registered User
Join Date: Sep 2006
Location: Las Vegas, NV
Posts: 241
Likes: 0
Received 0 Likes
on
0 Posts
I think it's pretty clear for the 48RE. Idle in Neutral (with the parking brake on). Or better yet, get a better flexplate, converter and tranny with a valve body that will circulate the fluid in Park (and take a lot more HP and TQ). Then everybody's happy. 
Tony
Tony
12-04-2006, 04:13 PM
#22
Registered User
LVTony is not the first person I have heard about this from. Had several rebuilders tell me the same thing about a Dodge, Do Not idle in Park or risk your trans to what happend in the photos above. BTW this is why they say to check your trans fluid in N as the pump don't work in Park! It's been this way on all Dodge trannys from the 727 all the way up to our RE48
JMHO
JMHO
12-04-2006, 05:30 PM
#23
Registered User
Join Date: Mar 2006
Posts: 382
Likes: 0
Received 0 Likes
on
0 Posts
If you're in conditions that warrant High Idle then why would you be concerned about keeping the tranny cooled? If the truck isn't pulling anything and is sitting in cold weather I would think you want to put some heat IN the tranny?
12-04-2006, 06:57 PM
#24
Registered User
Join Date: Nov 2006
Location: Delta Jct Alaska
Posts: 277
Likes: 0
Received 0 Likes
on
0 Posts
Thats probably why we never hear of it...also I leave my truck pluged in after I start it (when its cold - 20 or lower)till I'm ready to go.
12-05-2006, 12:56 AM
#25
The problem is only partially with cooling. The other part is lubrication. Those are steel gears in a steel housing. The snout of the converter runs in a brass bushing. With the trans in park there is no circulation of fluid in or out, the pump and converter sit there and spin in the same fluid constantly and generate heat in less than a pint of fluid. What happens when you over heat ATF?
The cooling is needed for the pump and TC snout not for the rest of the transmission. Beside, on the 3rd gen trucks the fluid never gets to the cooler until the fluid temp reaches a certain point. It simply routes back into the pan at the junction on the side of the block.
Obviously there is going to be a lot less heat held in that area at -40 than there will be at +40 degrees. The environment is going to play a large part in how soon damage can occur so this probably doesn't happen as often in the northern climes as it would in AZ. Even if is cold enough to keep things from overheating you still run the risk of hot spots developing where the oil film is not as good due to the lack of pressure.
Bottom line is the stock setup is not good for extended idle at any time or temp.
12-06-2006, 08:26 AM
#26
Registered User
Join Date: Sep 2006
Location: Northern VA
Posts: 798
Likes: 0
Received 0 Likes
on
0 Posts
Okay, based on the schematics in the service manual (the hydraulic schematic shows pressure to the TC in Neutral), I understand that there is no fluid pressure to the TC in Park, and the only lubrication and cooling fluid available is what's already in there - not much.
I will idle in Neutral... unfortunately, my high idle doesn't work in Neutral.
So I may as well just not take the time to idle in the mornings at all - just use the block heater and drive off.
I will idle in Neutral... unfortunately, my high idle doesn't work in Neutral.
So I may as well just not take the time to idle in the mornings at all - just use the block heater and drive off.
12-06-2006, 08:38 AM
#27
Registered User
No, it does NOT circulate the same in park as neutral. The 48RE DOES NOT circulate fluid in park unless the VB is modified. Feed to the TC and the cooler are both 0 psi. Extended idling in park will destroy the pump gears and the TC hub.
The quote from the manual references power flow NOT fluid flow. Check the FSM, it clearly defines fluid flow in all the gears and what components are used.
Here is what happns when you idle too long in park:
The quote from the manual references power flow NOT fluid flow. Check the FSM, it clearly defines fluid flow in all the gears and what components are used.
Here is what happns when you idle too long in park:
Nice, were these from your truck?? I'll bet that made your day!!
12-06-2006, 03:38 PM
#28
Registered User
12-06-2006, 03:55 PM
#29
Registered User
i think now DC wants you to leave it in neutral, and use the "stick & seat" trick on the brake pedal 
it just worries me to pull in with a HEAVY load on it at a rest stop, and leave it in Neutral to circ fluid thru the tranny while i run in. hate to chunk it in park & let it set there at pulling temps, with no fluid circ'ing
FWIW, this gets posted up about once a month, but the diagrams & pics are the best data i have seen so far.
it just worries me to pull in with a HEAVY load on it at a rest stop, and leave it in Neutral to circ fluid thru the tranny while i run in. hate to chunk it in park & let it set there at pulling temps, with no fluid circ'ing
FWIW, this gets posted up about once a month, but the diagrams & pics are the best data i have seen so far.
12-06-2006, 08:08 PM
#30
Registered User
i have also been told they do not circulate fluid in park which i do believe to be the case. my tranny temps will go up 20 degrees almost instantly-from shifting from neutral to park-when idling!