This weekend I replaced the cooling lines on my 700R4 and decided to do an experiment. I connected the stock in-rad cooler alone and went for a drive around town. The fluid temperature in the pan reached about 210 F pretty quickly and stayed there. I returned home and connected the auxiliary cooler inline after the factory cooler. It's some kind of small, cheap 4-pass copper and aluminum thing in front of the rad, nothing fancy. I went for the same drive but this time the fluid only got up to about 160 F, and cooled back down to around 150 F when I got back on the highway.

 

That's sweet. It brings up an urgent question: I just bought a Griffon radiator without the tranny cooler by mistake, and it should be here today. Do you think I can keep the radiator and run an external one only, or should I send it back?

 

I would just run the largest external cooler you can fit.

 

Will do. Thanks.