2001 Excursion, Stock tune, all stock except 4" exhaust.
Towed a 6x12 two axle enclosed trailer today 60-70 mph on interstate, oil and trans (were) staying around 218F with 86 deg outside all day.
Until... came to a section of road with stop and go traffic and rolling hills with about 30mph max and about crapped my pants when i looked over and saw that the trans had reached 250F and there was no where to go... wall to the left wall to the right...
This went on for a few miles before getting back to speed and set the cruise at 55... it took about 15 or 20 miles to drop back to 230F and stayed there another half hour until i could stop and idle while i picked up some scout parts.
Noticed the fan clutch fully engages when both temps reach about 210 deg range and road speed slows, radiator is 2yrs old, previous owner installed radiator without transmission coolant loop in it.
About 5k ago i flushed the trans with schaeffers, replaced filter and had flow to spec through the fluid/air cooler. No leaves or debris b/t coolers radiator etc...
Will a 6.0 trans cooler upgrade alone get me back to good temperatures or do i need to add in a radiator that includes the trans cooler loop?
Trans is a rebuilt unit with thought to be 60-80k on it.
The trip back home with more downhill and less stopped traffic both oil and trans stayed b/t 215 and 220 same 60-70 mph.
I-20 from augusta ga 20/285/575 to canton these weren't huge hills either.
Thanks for replies.

 

 

I believe the 6.0 cooler is about TRIPLE the cooling area. General advice is if you're going to tow, upgrade your trans cooler, with the 6.0 being a very popular option

A question you should ask now...is your trans fluid okay with the overheat? (Sorry, I don't remember the numbers)

 

Its still bright pink on the stick and dabbed on paper towel smells like automotive perfume just like when it went in.
I presume that fluid loop in the radiator can shed a lot of heat into the coolant if you are towing like that with a stock trans cooler.
I run 200-210 in high 90deg weather unloaded. Figured it was from having only an air cooler but never expected to see 250, I seldom travel farther than 10 miles away towing anything.

 

Dang. If you run that hot unloaded, I start to wonder if your temp sensor is messed up somehow. I have only seen my bone stock 4r100 reach 210 once when I was in my extreme tune going uphill onto interstate and really laying into it. I was unloaded. It jumped from about 185 to 210 and I let off. About 92 degrees outside.

 

And there is the root cause of the high temperatures. The radiator cooler does most of the ATF cooling. The little aux cooler you have left is only designed to take the temperature down a small amount. It isn't capable of cooling the transmission on it's own.

It may. It will probably be fine, but the conditions where you may still get hot is lower speeds, with rolling hills, and stop and go. That's where you really need a cooler in the radiator.

250F won't destroy the trans fluid, contrary to popular opinion.

His isn't stock. The previous owner removed most of the transmission cooling.

 

^^There you go^^

Thanks, Mark. I believe you posted something a while back...'at xyz temp it can go all day, above that it can go 20 mins' or something?

Sorry, I'm a bit sketchy on my recall at times

 

I wouldn't be terribly worried about hitting 250, but at that point I would start keeping a close eye on it to make sure it didn't continue rising. You need to get the right radiator, this should keep it under control for most conditions. The couple times I got stuck with a heavy load and slow hilly traffic I dropped into 4low with the hubs unlocked, that took the load off the torque converter. Only problem is that when the traffic opens up you'll have to stop to safely engage high range before you can speed up. I think manually shifting into 2nd will allow the converter to lock up rather than it shifting to 3rd and not locking. Most of the heat is generated in the converter. If the speed is too slow to reach 2nd gear lock-up keep it in 1st and let the engine rev higher, less load on the converter and more air pulled by the fan.

 

"The radiator cooler does most of the ATF cooling."
Thats the problem then, ill replace the radiator.
Thanks to all !

 

You can go as high as 220F all day long with no problems. You can go up to 250F for up to a half hour at a time.

Just to be clear, the correct routing is from the front of the trans to the radiator, then to the aux cooler, then to the rear of the trans.

 

Amongst that routing, where would it be safe to install an external filter?

 

My rig must be the exception, still have the little OEM....never have seen 200 degrees.

 

Well, what do you expect when you haul a TINY little thing like that around! :P LOL.

 

Install it in the line from the front of the trans to the radiator.
But you also have a cooler in the radiator. That makes all the difference.

 

I dunno what's up but my E99 still only has stock stuff but has a deep alloy pan and I'm concerned that my tranny runs too cold, it just gets warm when towing heavy.