We recently noticed a puddle of transmission fluid under our 1999 Grand Caravan. On closer inspection we found that it was coming from the radiator overflow, meaning that the transmission cooling loop in the radiator must have ruptured allowing transmission fluid into the radiator. I have an external transmission cooler and was wondering if it would be okay to simply block off the transmission fluid lines going into the radiator and reroute the lines form the transmission so that it only uses the external transmission cooler.

I would think as long as you are not towing anything it may be ok. The only thing I would do would be to move the cooler in front of the Rad so that it gets cool air, but I think it may be pushing it!

A new rad is about $400 Cdn, but you can get a rebuildfor an\bout $200. thet would be the best route, a lot cheaper than a new tranny!

If you have an external cooler that is a supplement to the radiator cooler you may want to replace both with a larger cooler. It is alright to block the lines to the radiator but I would remove the lines at the radiator and block the holes with pipe plugs. Make sure you flush the cooling system and refill with new coolant due to the contamination of the transmission fluid. Also you may want to change the fluid and filter in the transmission just in case you got any water in the fluid.

Well, to be safe I replaced the radiator because I had concerns whether the stand-alone transmission cooler would be sufficient.There was a lot of antifreeze forced back into the transmission so I drained and then refilled it three times to flush it out. I suspect that the torque converter is holding a lot of contaminated fluid and that makes it very hard to easily remove it. Is there an easy way to drain the torque converter so that I wouldn't have to flush many times (just in case this ever happens again - haha).

Not really, of course you could drop the transmission and remove the torque convertor and then dump the fluid. (just kidding). Just keep an eye on the transmission and change the fluid and filter again after about 10K miles. Of course you could install a drain plug in the pan and just drain the fluid rather than having to remove the pan each time.