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      09-17-2012, 09:07 AM   #17
ajm8127
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Drives: '07 335i
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Location: Pittsburgh

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I believe as the temperature of the ATF increases, the life of the transmission decreases exponentially. I read the entire chapter 2 out of the Google book (Handbook of Lubrication and Tribiology: Volume I Application and Maintenance) I posted over the weekend, and it was informative.

From what I've read, the "lifetime" fluids are designed to change very little in viscosity during their life. So a good indication of the health of the transmission may be to do regular UOA on the ATF to spot trends in the change in viscosity.

My reading also seems to indicate that oxidation of the fluid is very bad (sounds obvious) "with temperature being the key factor". Oxidation will cause changes in the viscosity characteristics, formation in insolubles (sludge, varnish, etc.), internal corrosion, and failure of seals.

I would say if your fluid spends any time above this "critical" temperature as read with the Bav Tech tool or others, it should be changed. Also, it looks like a trans cooler is a necessity for an AT car that is tracked to prevent these high temperatures.

Because the ATF is expected to do so much (transfer heat, lubricate, transfer power, prevent corrosion), the health of the AT is directly linked to the health of the ATF. So the easiest way to ensure your transmission lasts a long time may be to change the ATF regularly.

A second option would be the trans cooler if you plan to track the car, and if you decide to go pretty far to increase the torque output of your engine, an upgraded valve body or high performance clutch packs might be a good solution. Both Level 10 and IPT offer a service to upgrade your valve body, and both also offer rebuild kits.

Level 10 also has some sort of software upgrade for sale. I wonder what exactly that is.