Trans cooling question

[KJ Ryu]

I just replaced the radiator in my QT'd J10. This truck came to me with an external trans cooler, mounted about 1/4" to 1/2" in front of the radiator but still piped through the stock radiator, as well. Replaced the radiator tonight but I was in a bit of a hurry, using the company shop after hours, so I bypassed the radiator's internal trans cooler, using only the external cooler. Does this sound okay or do you think I should hook it into the new radiator, like it was, as well?

[Tatsadasayago]

Since you live in cold country I would suggest you use the built-in cooler as it will help the trans warm up faster in the winter.
Unless you are doing hard towing or extreme wheeling, the stock cooler can handle the job. I run both here in hot country and simply place a winter cover behind the grille when venturing out when it's below freezing.

[KJ Ryu]

Hmmm, good point. Thanks. Hadn't really thought about WARMING a transmission, before.

[Tatsadasayago]

I learned about over-cooling automatic transmissions in a very embarrassing and expensive way years ago.
I was working at the Reno Jeep dealership and did a full rebuild on a TF-727. I added an external cooler the customer requested at that time, road tested and sent the jeep on it's merry way. This was the 23rd of December and the customer was heading to Utah for the holidays.
That evening the service manager woke me up and told me my new trans rebuild was DOA on some mountain pass in the eastern Nevada mountains and the customer demanded my head on a platter.
Since I had a friend with a repair shop nearby I asked the customer to have the jeep towed there and I would drive out to fix the problem so he could get to his destination in time. I stuffed the Cherokee with every tool, part and supply I would need to do a full overhaul and beat feet out of town as fast as I could on the snow-packed and icy roads. Oh, and the heater in my trusty Blair Jeep 1 didn't work very well and I froze my butt off the whole way.

I arrived in the afternoon and after enduring a vicious tongue lashing was told the transmission began slipping at high speed and on steep grades and failing completely atop one pass. I hooked up my pressure test kit and warmed up the engine.
All pressures were good and the bands and clutches engaged strongly. I took the jeep for a short test drive and it shifted perfectly.
I was stumped.

After another hour of testing and poking around I took the jeep for another test drive. I drove longer and farther as the sun set and outside temperature dropped I noticed the engine was running a bit too cool--like 150-160 degrees.
DING! The cooler was over-cooling at highway speed and causing the transmission fluid to thicken up to the point that line pressure dropped so much the clutch packs and servos were unable to hold!

I placed a thick piece of cardboard in front of the trans cooler, checked everything once again, road-tested and sent the customer on his way. I told him I would stay at the shop overnight and he should call me immediately if he experienced any more problems with the transmission.

I didn't hear from the customer so I boogied back to Reno--missing Christmas day with my soon-to-be Ex-Girlfriend...
On the 27th, my birthday, I got orders to active duty for what became Desert Shield/Storm and was gone for almost two years.
I later heard that transmission lasted over 80k miles before needing a rebuild...

Forgive the long story.

[KJ Ryu]

Well, that just made my newest issue easier to solve, then. One of the hoses running to the external cooler is cracked and leaking today. So, I guess I'm just gonna take it out completely.

[KJ Ryu]

AND done! I think the only leak left now is from the rear axle. I think that's just the rubber fill-hole plug, though.

[will e]

Tatsadasayago, you know more about this than I do for sure but if overcooling a transmission can cause that kind of problem how is it that all of mine operate pretty much normally even when I start up at almost freezing temps and just drive away?

Not that I don't believe that there is a good operating range for the transmission.

[Renodemona]

I run a separate cooler. Aluminum air fin style Like you'd find on a sand rail. It's mounted on the side of the passenger side frame rail with the bottom fin sticking down just below the level of the rail with a skid on the bottom of the rail itself to protect the cooler. Been all over the place and haven't had any problems at all. Might be an issue if I bury it in snow or something.

http://www.ebay.com/itm/ALUMINUM-UNIVER ... 85&vxp=mtr

Mine's red though.