Coolant in Trans lines?

[natenkiki2004]

My concern:
I see fresh coolant "seeping" from the upper transmission cooler line going into the radiator.

From everything I read on here, the ATF pressure should be high enough that if the radiator tank (or gasket?) were to break the barrier between coolant and ATF lines that ATF would seep into the coolant, not the other way around. Also, from what I can tell, my fluids are not contaminated in any way. Getting everything up to temperature, the oil is a dark brown with no bubbles or grey/white color, the trans dipstick is a clear red, and the coolant in the overflow and cap is a clear green.

What is going on? The other day I wiped the area in question down and since then have driven it once. On the lip right below the fitting, there's green fluid. Looking up from that, the only area it could have come from is the trans fitting which is also wet. I will get a picture and/or video tomorrow when it's daylight but I'm rather curious on people's opinions on this. I do know that the trans line leaving the radiator goes to another cooler (aftermarket?) and then back to the trans. I've been thinking about bypassing the radiator but I'm not sure if the other cooler is large enough for the trans.

 

[natenkiki2004]

I think I just realized that the larger nut on the transmission line inlet is to seal the line to the coolant tank. I've never had a radiator apart but am I right in assuming that the trans cooler line is submerged into the radiator tank and is "bathed" in coolant? So it could be that it's just seeping out from that nut and that the fluids are still separated inside the tank?

*EDIT*
I envision something like this:
http://www.agcoauto.com/content/images/cooling/radiator_tank_core_transmission_cooler.jpg
Am I right in thinking those larger nuts on the transmission lines are simply to tighten the trans tank to the inside of the rad tank?

 

[2000StreetRod]

low pressure ATF cooling loop

Your transmission is probably similar to my 5R55E. The external ATF cooling loop has very low pressure and it is quite possible that hot engine coolant can flow into the ATF. However, in your situation it sounds like you just have an ATF leak at the fitting. This frequently happens when the ATF external connection is tightened or loosened without the use of a "backup wrench" on the mating connector.

You may be able to tighten the large nut that holds the female port against the tank internal seal to reduce or eliminate the leak.

Many of the stock Explorers came with the auxiliary external ATF cooler. It may have been part of a towing package. The cooling capacity is inadequate by itself. I tried two of them in parallel and used the radiator internal ATF cooler for cooling engine oil.

The ATF temperature was too high in the summer. The radiator liquid to liquid heat transfer is much greater than the auxiliary liquid to air heat transfer.

 

[natenkiki2004]

Makes sense. I wondered why the extra trans cooler had nice bent metal piping, it probably came from the factory. I always thought it was an oil cooler until I followed the lines. I looked at your remote filters & coolers thread, it's giving me some ideas

I'll give a try at tightening that nut although now, after driving, it's bone dry. Maybe it starts to seep as it contracts with cooling?