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      09-07-2017, 11:15 AM   #8
New to BMW ownership

Drives: 2010 black 128i auto
Join Date: Apr 2016
Location: Portland, OR

iTrader: (0)

Originally Posted by rjahl View Post
What makes the OP think the trans overheated? Did he get a warning on in the Kombi? I'm pretty sure the trans overheat will just lock you into a gear and throw a gear warning light without a power cut.

I would not change to a high temp fluid. The transmission is designed for a specific fluid with specific friction coefficients and viscosity. Anything other than OEM fluid will not work correctly. In any case, it's the hi temps you need to avoid. I do recommend changing fluid every 50,000.

Before I modified anything, I would check to insure that the cooling system is working like it should. I'm pretty sure you have a trans cooler built into the radiator and take note that there is a thermostat in the radiator that controls the trans fluid temp.

Regarding the trans tune , I've learned a lot about the ZF transmission and one item of recent discoveries me is the Torque Converter Clutch operation. It seems like the TCC spends a crap load of time in a "modulated" mode where the clutch is only partially engaged. Any constantly slipping clutch can build up a bunch of heat that the cooling system will need to deal with. One of my next experiments will be to lock up the TCC sooner and try for a full time TCC lock up in manual mode.

Recent logs in my Z4 show the TCC never locked up through a full 0-80 MPH WOT run that included 7,100 RPM shifts. Normal driving in 6th gear have the TCC in modulated mode up to 2,500 RPM where it registers a full lock up.
Thanks for the advice!

I'm not getting a CEL/gear warning light. I'll try pulling codes with my Carly but I don't think I can make it to any more track events before the rains/winter come. Maybe there will be some stored though. We tried pulling codes before and couldn't find anything using a scanner but my Carly found a few codes but I had believed unrelated to trans/overheating but could have been wrong. Any ideas which ones they might be?

Trans cooler is built in to radiator. Extra cooling systems seem to help a little or sometimes for some others facing this issue IIRC, but they cost $700+ (IIRC). If I could know it would help I might go this route but might rather save that money for a dedicated track toy.

The reason I believe it's overheating is that I read about these issues on the e90 forums, that the transmission won't shift easily nor allow power delivery when it happens on track, but returns to normal after cooling down (Sounds like TCC/clutch?!). By removing lower engine/trans plastic shield and running heat on full blast I was able to drive it harder, longer before issue occurred.

I'm very interested in a tune/TCC fix if possible. Details?