I have a 94Z A4...i was wondering why driving in D (3rd) heats up the tranny fluid much faster then driving in OD (4rth)? and not even just driving in 4rth gear in OD..driving all gears in OD seems to take forever for my tranny to heat up to even 105 degrees. In D it heats to 105 much quicker...

Also my tranny fluid tends to stay around 105-110 and get no hotter...is this ok?

 

No. Driving in 3rd gear (D), the whole geartrain is turning in the same direction (no underdrive 1st & 2nd, or overdrive 4th), therefore it produces the least amount of wear & heat. Anytime you have a planetary turning (working), you are producing heat. The likely reason that it is heating up quicker in 3rd gear, is the torque converter is not locked up.