you got ya self a tranny cooler in the bottom of the rad it can happen that this can pin hole and the rad pressurises coolant in to the tranny its not a common thing but can happen fluid would be obviously overfull and milky gear changes get a bit funny too but it can kill a tranny if not spotted soon enough
Hi Bryn. I have had the same problem with an XJ, ZJ and a WJ. All 4.0 ltr. After discovering the problem with the XJ it was easy to trace the problem with the others. I had parked up on quite a cold morning doing some paperwork in the Jeep and thought I noticed a wisp of steam coming from under the hood. It was only momentary and I forgot about it. Happened again so I looked closer and saw a very small leak in the top left corner of the rad as you look at it from the front. It was only slight and had it not been a cold day I may not have seen it. Exactly the same leak occurred on the other two in the same place on the rad. Tried Rad Weld but it only helped for a while so each Jeep ended up with a new rad.