your trans cooler is leaking. That's the only place the 2 fluids cross paths

 

I was looking into that, but when I search "transmission cooler" it seems like they are different (like mounted near radiator). I traced the lines and they meet at what looks like the cooler but it's mounted on the block near the bell housing. The lines look much bigger than the replacement coolers I am seeing.

 

There are two...the one on the block is actually a heat exchanger meant to bring the fluid up to temp...and that's your culprit. There's probably coolant in your trans fluid as well, which will mean a rebuild. Sorry man.

 

A total transmission rebuild? Wow, that sucks! I was hoping for easier!

If I could resize, I'd upload a pic.

 

If there's coolant in your trans fluid, don't drive it, tow it, and get it fixed...you might be able to avoid a teardown and rebuild depending on how long this has been going on.

 

the coolant basically "unglues" the clutches for lack of a better term. Might limp it around for a while but, it is toast. Again sorry!

 

threw a rod in my 2004 5.9 195,000 miles got a motor from junk yard with 110,000 miles. Had my tranny replaced 10,000 miles ago anyways, got it in fired up and while letting motor warm up checking fluids and everything noticed transmission fluid started going from red to pink, took cap off radiator and noticed tranny fluid was getting in water. so tells me my heat exchanger failed internally. All that work and now tearing back into it wishing i would of bought a new one instead of taking used heat exchanger from junk yard, now i know. Engine didn't run for more then 15 -20min, i had no coolant in yet just water because was about to flush the coolant system. Did i hurt my tranny at all? Have it drained going to do some flushing tomorrow. ordered the part #4337537 exchanger from cumminspartsdirect for 327.24 which is a fair price compared to 903 from dealer. whats the best way to flush my tranny without having to pull it? Any suggestions and help are greatly appreciated!!! had no coolant what so ever so is water only less harmful to the tranny?
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at least it was not antifreeze! I don't think water is as harmful, if it was me I'd drop the pan , re-install add fresh oil, remove the tranny cooler line, start truck and watch what is pumped out, soon as flow starts to slow down, stop engine and repeat by filling the tranny pan again. you might have to do this a few times. note do this in neutral (not park)..

or tow it somewhere where they can hook to a machine to flush it

 

My trans made it about 6k miles before the rebuild... clutch material in the pan. Mine failed on the way to the trans shop, strawberry milkshake coming out of the overflow bottle. Thought that since it happened on the way to the trans shop maybe I could dodge a bullet. No such luck. Had the trans shop do the flush and bypass the heat exchanger then tried to find a shop to flush the motor. That proved to be more difficult than one would think. None of the shops wanted trans fluid in their flush system. Found a shop that had a tank they emptied into a larger container and they had no problem doing it. The hardest part was getting all the gunk out of the radiator, the flush would not get it all. So I went to harbor freight and bought a cheap vacuum pump, put both hoses into a milk jug cap, sealed the cap and used the container to hold the crap coming out of the top of the radiator. Took a long time to get it clean and 2 more flushes at the shop later it was all out. PITA!

IIRC the 6.7's dont have the heat exchanger... buy the MT blockoff plate or bypass it, rebuild the trans when the time comes and move on.