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      11-15-2012, 11:34 AM   #19
ajm8127's Avatar

Drives: '07 335i
Join Date: Aug 2012
Location: Pittsburgh

iTrader: (0)

Your estimations for the ATF temp exiting the stock cooler make sense when you consider they correspond with the 108C and 95C temps of two of the operating modes for the cooling system. I have noticed 108C temps in stop and go driving, and around 95C temps in normal driving with my driving style, which is on the slightly more aggressive side. This is the temperature of the water exiting the head. Of course the temp of the water entering the water to oil heat exchanger will be lower because it has just passed through the radiator, but you can't expect the heat exchanger to bring the ATF temp all the way down to match in inlet temp of the water. That is unreasonable.

I also would not expect your oil or water temps to change with your setup because you are cooling the ATF after the stock heat exchanger, so the same amount of heat is being transferred to the water as before. The only difference is the AFT returning to the transmission is now cooler. However, if you are putting cooler fluid into the transmission, the fluid coming out should be a little cooler as well, which may translate into slightly cooler water temps. Time will tell.

I am curious to see what happens at the track with your setup. Obviously your ATF temps will be lower. You said in the other thread that you've never had a problem with limp mode, and I wouldn't expect you to this time especially considering it is November, and ambient temps, and more importantly, track temps, will be lower than in July during a sunny day.

Component protection starts at 117C (234F) so as long as your water temp at the heat outlet is below that, you should be fine. After this the engine output is reduced, which is not what you want at the track.

Regardless, have fun.