Question for the community. I replaced my radiator and my car has an external transmission cooler. The new radiator is bigger, and i’ll need to run new lines to the external cooler. I’m tempted to just get rid of the external cooler and hook the lines to the new Radiator. Is this a bad idea?
Depends on wether you tow a trailer a lot or have a higher than normal stall speed torque converter.
nope, just troll around the neighborhood 
use both!
I’m fascinated that this is a good idea… My Jeep (WJ) has this configuration and folks on that forum see leaks and issues with coolant/trans fluid mixing every so often. I added an external trans fluid cooler to it and deleted the radiator circuit instead…
That’s just the fault perspective.
Concerning performance, I’m also skeptical that the radiator (full of hot coolant) with an integrated trans fluid cooler is going to do a better job of cooling off trans fluid than a seperate cooler.
I could see the practicality of a cold and very cold environment doing the warmup for the trans fluid but once all is up to temperature, no way it’s a better setup, right?
I have a dedicated transmission cooler that came out of a Probe. Two of the integral mounting points on the cooler match factory holes on my Cougar. The third mounting point uses a common L-bracket that mounts to another factory hole on the radiator support.
I ended up doing what the factory did. I put in a bigger radiator and I’m not towing. I think I have it all done now.