ATF flow to coolers whilst in "Park"????

[Doctor W]

It's been my habit to run my Jeep at idle in "Park" for say 1/2 to 1 hour at a time to recharge the batteries if I'm camped for more than say 1-2 days in one place (i.e. haven't driven anywhere for a couple of days)......I get about 40A @ 13.4 -13.8V which is great for a quick partial recharge of my AGM's.

Now I have recalled reading somewhere that Jeep auto transmissions don't "pump" when in "Park" and thus there is no fluid flow through to the in-radiator and auxilliary oil coolers.

When you check the ATF level in my 42RE type tranny, you need to go thru all positions and then check fluid level whilst idling in "Neutral" ( NOT "Park") to get correct reading.

Apparently fluid does pump in "Neutral" (and in "Drive" and "Reverse" obviously!) but not in "Park".

These Jeep automatics such as the 42RE, 44RE, 46xx, xxRH etc are a modern (4 speed overdrive and electronic controls) development of the old Chrysler Torqueflite 727 or 904 (not sure which) and these Torqueflite 3 speed autos were also used in Range Rovers prior to the fitment of ZF autos in 1986(?).

I used to own an early 3 speed auto RR and clearly recall the Owners Handbook warning NOT to run the vehicle in "Park" for extended periods and not to rev it high in "Park" either.

The Jeep Owners Handbook doesn't give such a warning, but I'm just wondering if anyone knows for sure?......I don't want to cook my auto.

Any and all productive conversation eagerly awaited, thanks people!

 

[bob91yj]

The pump is driven by the torque converter which is turning any time the engine is running, so yes, you have transmission fluid flow through the transmission. The only difference between neutral and Park is the parking pawl is engaged while in Park.

 

[Doctor W]

The pump is driven by the torque converter which is turning any time the engine is running, so yes, you have transmission fluid flow through the transmission. The only difference between neutral and Park is the parking pawl is engaged while in Park.

That's what I thought was the case, but apparently not so in THESE model autos.

I kow I've got some fluid flow with engine running, but not thru cooler lines apparently.

But I want to know definitively.

 

[nely]

You wont cook your transmission in park. Wether the fluid is flowing thru your cooler or not. The fluid isnt pressurizing the clutches or working, so there is minimal heat build up in the transmission.

Sent from my SGH-T959 using Tapatalk

 

[bob91yj]

I'm 99% positive that you are getting cooler flow in Park, going to double check when I get to work today (I work at a dealership, we were a Jeep dealer until two years ago).

 

[JPK]

The 545rfe, a further development of the 42re is in lots and lots of police cruisers. They sit in park idling with a heavy duty, high output alternator providing power to their electronics packages - computer, radios, video cameras, spotlights...

 

[bob91yj]

Double checked with my transmission guys today, the 45RFE has minimal cooler flow at idle, but will not overheat the transmission in Park/Neutral.

 

[Doctor W]

I'm 99% positive that you are getting cooler flow in Park, going to double check when I get to work today (I work at a dealership, we were a Jeep dealer until two years ago).

Thanks, I'm looking forward to a definitive reply.

Also.......
.............I just read a Q/A column in the online version of Jp magazine, where a guy couldn't figure out how to connect an auxilliary trans. cooler. When he disconnected both hard lines at radiator tank to figure out which was in/out, he found he had no flow!... the reply was that the cooler lines don't have flow when in "Park" only in N, D, and R.......so this sorta confirms what I feared - but I think he was talking about a TJ (I'm not sure though) and they had the old 3 speed auto - not sure of its name.

Mine's a ZJ with a 4.0 and the 42RE transmission.

 

[Doctor W]

Double checked with my transmission guys today, the 45RFE has minimal cooler flow at idle, but will not overheat the transmission in Park/Neutral.

What about 42RE's ????...... which is what I have.

Thanks for asking, could you check again?

 

[JPK]

Dude, if you're worried about it put it in neutral with the parking brake set. If you're worried about that, chock it.

 

[redthies]

Since everyone is thinking auto tranny coolers, I have another question... I am having a shop put the new coils in my Rubi today, and have a B&M super cooler added as well. The one tech suggested we might have to delete the factory cooler to use the B&M. I think this is not the case, but can anyone shed some light on this? It is killing me to not do these jobs myself, but I am working 7 days a week to get my contracts all finished before our two week trip starts next week. I want the cooler in as part of the trip will see us pulling a 3000lb trailer up to Tahoe/Yosemite area. At least one of my contracts is building a house for the owner of the shop so I don't expect much if any bill for the work:sombrero:

 

[Hawkz]

You can continue to use the stock radiator/transmission cooler and put the extra cooler in line with it, or bypass it all together. The main reason to keep using the stock cooler is that in the winter the heat from the radiator will actually heat the ATF to help the transmission warm up quicker. You also get a slight increase in ATF volume, but I'm not sure it'll make a difference.

I decided to bypass the stock cooler and only run the B&M...

 

[Doctor W]

Dude, if you're worried about it put it in neutral with the parking brake set. If you're worried about that, chock it.

That's what I've been doing lately, but it's a hassle.......park brake is next to useless on a slope, so I've been chocking it.

People have told me all Jeep park brakes are rubbish - don't know if they meant tiny drums for ZJ parking or ALL jeeps...........Anyone know????

 

[Doctor W]

Since everyone is thinking auto tranny coolers, I have another question... I am having a shop put the new coils in my Rubi today, and have a B&M super cooler added as well. The one tech suggested we might have to delete the factory cooler to use the B&M. I think this is not the case, but can anyone shed some light on this? It is killing me to not do these jobs myself, but I am working 7 days a week to get my contracts all finished before our two week trip starts next week. I want the cooler in as part of the trip will see us pulling a 3000lb trailer up to Tahoe/Yosemite area. At least one of my contracts is building a house for the owner of the shop so I don't expect much if any bill for the work:sombrero:

My understanding is that the additional oil/air cooler goes in the circuit BEFORE the fluid goes into the stock radiator bottom/side tank. This is so if ATF is very hot it cools , throwing less of a heat load on radiator and also the coolant in the radiator then further cools (or warms up, if it's too cool) the ATF to correct operating temp before going back to auto gearbox.

It's not good to have ATF running too cold.

 

[JPK]

That's what I've been doing lately, but it's a hassle.......park brake is next to useless on a slope, so I've been chocking it.

People have told me all Jeep park brakes are rubbish - don't know if they meant tiny drums for ZJ parking or ALL jeeps...........Anyone know????

Mine holds the Jeep on a hill. Maybe yours needs adjustment?

JPK