So I tried to hook up the temp sensors to my PLX gauge a few days ago. It comes with 2 Molex connectors and you have to connect them by crimping. I did not have the appropriate crimping tool for Molex so one of the connectors came loose and broke off before I got good temps. However, I was able to solder instead of crimp the other connector. So that one worked. I am waiting for a new connector to solder from PLX Devices to finish off the job.
The good connector I chose to hook up to the outlet sensor to get readings from the RETURN LINE BACK TO the transmission AFTER the cooler. (So I do not yet have one for the temps BEFORE the cooler.) On a cold start, temps as expected slowly creep up to 140F and plateau for about 5-7 min there. Then they rise to 160F a bit faster (presumably when the T-stat is opening). They plateau there around 160-165 for another 10 min or so and then start to rise again. With driving for about 40 min or more temps range 165F-185F with an average temp of about 172F. Max temps I have seen are 199F over the last 3 days. This is in stop and go traffic in 77F degree FL weather. Since I do not yet have an inlet temp BEFORE the cooler I used the IR temp sensor again to compare. The INLET hose temp measures 165F and the OULET temp measures 135F when the temp sensor reads 195F. So, this suggests at least a 30F drop in transmission fluid temps through the cooler and that the hoses are reading about 60F LOWER than the actual fluid temp (outlet hose = 135F and actual oulet fluid temp = 195F).
Therefore, I BELIEVE the transmission fluid BEFORE the cooler is a whopping 225F (165F + 60F hose to fluid discrepancy) in stop and go traffic and averaging about 202F (172F avg + 30F drop across cooler) with everyday highway cruising. What I think makes this even more impressive is that my INLET temp sensor and transmission cooler are plumbed in series after the factory heat exchanger. So the exchanger has already done its cooling. It is also important to know that most widely acceptable temps for a transmission fluid is between 180-200F. The BMW factory setup seems to be significantly lacking here. You could argue that my cooler is TOO efficient by reducing temps to an avg 172F with daily driving which is below the 180-200F range I just described. However, I should mention that I did these series of temps with NO TUNE in the car. I am FBO currently but without tune since I took it out when I had my electrical problem I mentioned earlier. This is also with daily driving and only mildly spirited driving. I plan to push the car a bit more and see if temps rise much. I do not expect that they will since temps actually decrease as I go faster because there is more airflow across the cooler. Also, I will put the Procede back in and see if that changes things. I will also have to see how the temps compare on the track. I will likely not make it to Sebring before the year is over so this will unfortunately have to wait.
I know this is still somewhat preliminary data but I thought it was important enough to update anyone interested in this mod. I should know for sure when I get the new Molex connector and solder it in. It should arrive this week or early next week.
Lastly, you may be wondering how this compares to the Oil and Water temps. The oil temps never rise above 240F in my car with DD since I have the ER dual oil cooler. The Oil temps do actually seem to be about 7-10F lower since install of the transmission cooler but this may be just wishfull thinking. My Oil temps at the track run 250-255F max. Water temps run 204F - 214F with DD and avg 208F. With the transmission cooler these have not changed. At the track they avg. 215F and reach occassional bursts as high as 231F. This all suggests that the AT cooler I have installed should go a long way to helping the ATF stay cool at the track.
More data to come as I get it.