1999 750iL Transmission Fluid in Radiator

[maxumpower]

I just bought my first BMW! I got it cheap but i'm sure it was at a price to pay to fix it.
The bimmer only has 110263 miles.
It was over heating and the transmission goes into failsafe mode.
I have replaced the coolant bottle, temp sensor and cap, while doing this i noticed red milky crap in the radiator. I am also changing the thermostat because some jack A** took the thermostat out and the car was giving a code P1622 because it wasn't there.
So i am thinking that the radiator has a leak in it and trans fluid is going into the radiator. While pulling out the radiator i noticed that there is only one hose that connects to the trans cooler.
So my question or questions are has any body had this problem and do i just change the radiator or is the leak in the actual transcooler under the car?

[Binjammin]

This happens occasionally. The tranny cooler inside the radiator tank cracks and fluid contamination occurs. What you'll want to do first and foremost is to make sure you don't have CROSS contamination: check your tranny for coolant. If you're lucky, the contamination was only one way, and that'll be easier to clean up. If you have coolant in your transmission, you'll want to do a series of trans drain and fills in order to remove as much coolant as possible. Possibly even find a tranny shop that can do a flush for you, as coolant in the transmission is bad, it will wear your clutches out a lot faster than should happen.

You'll also want to pick up a new radiator (obviously) and drain and fill the engine several times as well. Some people use vinegar diluted with distilled water to clean the cooling system out, I like to use cascade and hot water, but either way, you want to run something through the engine to get rid of all the tranny fluid, then run a lot more water through it to make sure all the cleaner is out, then fill with the appropriate coolant of your choice.

[maxumpower]

Thanks for the info. What i have noticed with the radiator is that only water goes through the hose to the trans cooler. The trans fluid does not go through the radiator like most other coolers. I am unable to post a picture of the set up. I have included a link to a picture of the cooler.
http://www.google.com/imgres?imgurl=...kQ9QEwAg&dur=3

[kimokk]

Does yours have the part attached to the top called the "voltage regulator?" That is the part where coolant flows into. The two ports underneath are for the transmission lines.

It's item #2 in this diagram.

[psjr]

Facelift models have the separate transmission oil cooler (listed as "voltage regulator" in parts diagrams).
You will want to replace that as well as check for coolant in the transmission fluid.